Revolving Door Band

This is when a band becomes notable for a constantly changing lineup, with musicians coming, staying for only a few years (or even less than a year), then leaving.

The musicians' time spent with the band is important; just because most (or even all) of a band's lineup has changed doesn't automatically qualify it for this Trope--even if all those changes occur within a short time.

Here's a clarifying non-example of this trope: in less than a decade (1997-2005), all but one (Abdul "Duke" Fakir) of the Four Tops died or became too ill to stay with the band and were replaced (they were even a trio from 1997-1998). But during their entire run, they've had only seven members: the original four singers, and the three replacements (who are still with the group.)

It can be anything from a single position having a different musician from time to time, to the second type of I Am the Band, to its Logical Extreme: the group going through entire lineups on a regular basis. In short, it's a band that makes the phrase Musical Musicians not redundant.

NOTE: It is not unheard of for a band to fit both this and Long Runner Lineup.

Country

 * The Oak Ridge Boys originally played this straight, having consisted of several different men until the most familiar lineup (lead singer Duane Allen, tenor Joe Bonsall, baritone William Lee Golden and Basso Profundo Richard Sterban) came to be in 1972. Golden was replaced by Steve Sanders from 1986 to 1995, when he returned.
 * Nitty Gritty Dirt Band. Jimmie Fadden and Jeff Hanna are the only remaining original members.
 * Asleep at the Wheel. Ray Benson is the only original member.
 * Blackhawk was founded by Henry Paul (lead vocal/mandolin), Van Stephenson (guitar) and Dave Robbins (keyboards). After Van Stephenson left due to skin cancer, he was replaced by Randy Threet (who was previously in their backing band), then Anthony Crawford, then Michael Randall. Robbins left and John Coleman replaced him. Threet rejoined. Coleman left. The backing band got assumed into the main band. Robbins rejoined. Is your head spinning yet?
 * Shenandoah had a hard time keeping its members together after the mid 1990s. Keyboardist Stan Thorn left and Rocky Thacker replaced original bassist Ralph Ezell. They broke up in 1997 after lead singer Marty Raybon formed the One Hit Wonder Raybon Brothers and then went solo. Three years later, Thacker re-established the band with original guitarist Jim Seales, original drummer Mike McGuire, rhythm guitarist Curtis Wright, new keyboardist Stan Munsey and new lead singer Brent Lamb. Lamb left early on and Wright took over lead vocal duties. Thacker left and Ezell rejoined. Wright left and Jimmy Yeary took over on lead. Ezell died and Mike Folsom replaced him.
 * Highway 101 also had a hard time sticking to one lineup. This chart on their Wikipedia article says it all. And no, your eyes don't deceive you; the lead singer post alone really did go Paulette Carlson, Nikki Nelson, Paulette Carlson, Chrislynn Lee, Nikki Nelson.
 * Dave & Sugar consisted of lead singer Dave Rowland and a revolving door of female backing vocalists, some of whom sometimes shared the lead vocal.
 * Vince Vance & the Valiants. There have been literally dozens of Valiants, including the aforementioned Chrislynn Lee. Amusingly, one of said Valiants (Lisa Layne) got the lead on their most well-known song, "All I Want for Christmas Is You" (not to be confused with the Mariah Carey song).
 * Exile's shift from pop-rock to country started in 1980, around the time original lead singer Jimmy Stokley was replaced by Les Taylor. Taylor and founding member J.P. Pennington both left for unsuccessful solo careers in 1990, with Mark Jones taking over as lead vocalist, and the group disbanded in 1993. Many of the 1980s members, including Taylor, rejoined in 1996. Meanwhile, many of the backing musicians shifted as well. Most notably, Mark Gray had four Top 10 country hits in the mid-80s, and wrote number-one hits for Alabama, Janie Fricke and Gary Morris.

Gospel

 * The Blackwood Brothers. While it's no surprise that the entire original lineup has been replaced after 76 years, no single lineup seems to have lasted more than a few years.

Jazz

 * The Sun Ra Arkestra. Sun Ra would fire a musician by gathering the band together--minus the fired musician--and skip town, leaving the musician stranded. The U.S. State Department finally had to order him to at least bring musicians he fired back to the United States instead of leaving them stranded in a foreign country.
 * The Squirrel Nut Zippers

Metal

 * Cradle of Filth. The longest-lasting lineup lasted only two years. Dani Filth is the only constant member.
 * Trope Maker of Grindcore Napalm Death are an extreme example. The founding duo split up before recording their first album; the remaining founder member lasted until the end of side one of the band's debut album before leaving, at which point the entire band had been replaced. The only bandmember who appeared on both sides of the group's debut album was blast-beat drummer Mick Harris, who left two albums later, at which point the entire band had been replaced again.
 * Iron Maiden, as the documentary The Early Days, Part 1 has shown. There were many lineup changes before the first album in a 5-years span. After their first album the band had many other lineups which included three singers, four guitar players, and two drummers. The only constant members were Dave Murray (guitar) and the bassist/founder Steve Harris.
 * Therion consists of Christofer Johnsson and whoever he's convinced to work with him on the latest album. See for yourself.
 * Van Halen did this with lead singers. The original (and current) lead singer was David Lee Roth from 1974 to 1985. Then Roth left and was replaced by Sammy Hagar from 1985 to 1996. Though a reunion with Roth was teased in 1996, Hagar was ultimately replaced by Extreme front man Gary Cherone for three years and one album. Hagar reunited for a tour and three new songs on a Greatest Hits Album, and then Roth finally rejoined the band for a tour in 2006 (an album is expected).
 * It should be noticed that the first two still fit Long Runner Lineup. Bassists had a minor case: Michael Anthony was preceded by two guys in 1972 and 1974, and succeeded by Eddie Van Halen's son Wolfgang in 2006.
 * Black Metal bands are constantly switching line-ups. Controversial group Mayhem have had so many line-up changes that Wikipedia has an entire page just for the effort of chronicling the member line-ups.
 * Gorgoroth are also an example.
 * No one really know what the glue is that keeps the name Zao going on, but albums keep getting made.
 * Warrant, the band that made Cherry Pie, has had around 2 dozen musiciance since 1984, and no lineup has lasted more than 2 years. Only guitarist Erik Turner and bassist Jerry Dixon have been around since the beginning.
 * Lordy, Lordy, Lordi. The longest-lasting lineup lasted only 3 years.
 * Friggan Otep. Otep herself is the only remaining member, and they have not had a consistant lineup that has lasted more than a year.
 * The Dillinger Escape Plan: They usually work as a five piece, and have had three rhythm guitarists, one vocalist, one bassist and two drummers leave over 13 years or so. Lead guitarist Ben Weiman is the only current member of the band from the original lineup, and even he very briefly quit once. In two separate cases, members have been forced to leave due to medical injuries rendering them unable to play their instruments: Original bassist Adam Doll was paralyzed from the chest down in a car accident, while guitarist Brian Benoit suffered nerve damage in his left hand. Benoit may or may not end up returning to the band - he's able to play guitar again, but can no longer play it at the technically-demanding level required by most of the band's material.
 * Anthrax has been like this. Since releasing their first album, the only two members who've been in the band the whole time are guitarist Scott Ian and drummer Charlie Benante. They've had four singers, two bassists (one left, and came back, with the other filling in on live performances while the first was gone), and two lead guitarists, plus several guitarists who recorded in the studio but were never official members of the band.
 * Rose Funeral have been a band since 2005. In that time, 18 members have joined and left. Very few have anything good to say about the personalities of the core members.
 * Periphery have also been together since 2005. Thanks to a recent shedding of members, the only remaining founding member is Misha Mansoor, and they have particular difficulty retaining singers - they don't even average a new one every two years, having had four in their seven-year life.

Pop

 * Menudo. As a long-running, producer-created boy band, its lineup would change whenever a member grew facial hair, went through a voice change, grew too tall, or turned sixteen, whichever came first.
 * UK newspapers actually more or less invoked this trope when the last original Sugababe had a breakdown and "quit", which meant Sugababes replaced all three of its original members over the last 12 years or so. To add to the Sugababes mess, as soon as the last original member (Keisha) left, there was immediately talk of the original three reforming as a new band, which is looking increasingly likely.
 * The Pussycat Dolls

Punk

 * Andrew Jackson Jihad, which has only two constant members.
 * The Fall are well known for line-up changes, the only constant being Mark E Smith, who once said of the ever-changing line-up "if it's me and your granny on bongos, it's a Fall gig."
 * A man wrote a book about trying to find all of the ex-members (there were fifty). That said, the dynamic duo of Craig Scanlon and Steve Hanley held down the fort from 1979 'til 1995, which is damn impressive.
 * The lineup of Black Flag flip-flopped so much that they'd occasionally have random audience member join the band because someone quit on extremely short notice.
 * Horror-punk group The Misfits have had some 17 different members in only about 20 active years. Though many people would consider Glenn Danzig the band's face, he actually never spent that much time with the band.
 * Irish Punk band Stiff Little Fingers have gone through four drummers, three bassists (including losing their original bassist just before they got a record deal and replacement Ali McMordie leaving in the early 90s and coming back in the late 2000s) and two guitarists in their time together. Only lead singer, guitarist and lyricist Jake Burns has been a constant member.

Rock

 * Green Jelly is Bill Manspeaker and a parade of others. The lineup that recorded the band's Top 40 hit "Three Little Pigs" included Maynard James Keenan and Danny Carey, the two of whom later formed Tool.
 * There aren't any original members left of Rockapella.
 * Sha Na Na has only two original members left, out of 15.
 * While Deep Purple would seemingly fit in I Am the Band, considering that Ian Paice was the only constant member, it fits more here due to Paice being the drummer and not the Face of the Band (vocalist Ian Gillan has been in all Marks except I, III, and IV; and guitarist Ritchie Blackmore was in the band until Mark IV, then left for good replaced by Steve Morse).
 * Purple was originally conceived as a project called "Roundabout", a band which would allow musicians to "get on and off" as they pleased.
 * King Crimson is the King of this trope. In the 41 years they've been around, they've had 19 members (not including recording/touring guest musicians, with which the number would climb to about 30) pass through, around, and back to the band, only one of which being Guitarist Robert Fripp; he's the only member who is still with the band (and he didn't start making major songwriting contributions until the band's fourth album)- it's so complicated that The Other Wiki resorted to using a table. Now he's become the band, but only partly by default, as by his words "King Crimson is a way of doing things" (of course by this point his influence on the band's writing is undisputable).
 * James have had somewhat of a revolving door lineup; Glennie, Gilbertson and Whelan were first up, then Booth came in, Gilbertson left, Gott came in, Whelan left, Baynton-Power came in, Davies, Diagram and Hunter came in, Diagram left, Gott left, Kulas and Oxxal came in, Booth left, Booth came back, Booth left, everyone left, Glennie and Gott restarted the band six years later, Booth came back, then finally Baynton-Power, Davies, Diagram and Hunter all came back (yes, that does make a lineup that already happened at one point). And I'm sure I'm missing somebody. Jim Glennie--the bassist--is the only relatively constant member.
 * Yes has had a rotating cast of musicians in all positions, except bass (which has always been Chris Squire).
 * It got so ridiculous, Wikipedia actually has not one, but two charts for tracking the ever-shifting lineup.
 * Asia has even had musicians join and leave without ever recording.
 * Marillion up until 1984. They also had three different vocalists in 1989, but their lineup has remained stable ever since.
 * The Grateful Dead certainly had a revolving door when it came to keyboard players.
 * The Sisters of Mercy; Andrew Eldritch is notoriously hard to work with, and he's the only original member left.
 * The Red Hot Chili Peppers. 14 members in 27 years, and only briefly did the band tour with more than 4 members. Although, in all fairness, two of the four members (Anthony Kiedis and Flea) were founding members who never left . And current drummer Chad Smith has played with the band since 1989.
 * Emerson Lake and Palmer are a unique example. The original trio lasted from 1970 to 1978. After a several year period, keyboardist Keith Emerson and vocalist/bassist/guitarist Greg Lake and Rainbow drummer Cozy Powell as Emerson, Lake & Powell., from 1986-1988. Lake & Powell would leave, Palmer would re-join, and Lake would be replaced by vocalist/guitarist Robert Berry (not, as you might expect, as Emerson, Berry & Palmer, but as 3). by 1992, the original ELP would reunite, break up in 1997, and return in 2010 for reunion shows in the UK and Europe.
 * Likewise, Crosby Stills And Nash. They began as CSN, added Neil Young in 1970, broke up in 1972, and would semi-reunite in splinter groups (Crosby-Nash, and briefly the Stills/Young band), and appear on each other albums through the 1970's. CSN would reunite in 1977, disband in 1984, then return in fits and starts as CSN, CSNY and occasionally Crosby-Nash from 1988 to the present day. :)
 * Jethro Tull has had bandleader Ian Anderson from the beginning, and guitarist Martin Barre since 1969. Much of the band's history has revolved around Anderson, Barre, and various keyboardists, bassists and drummers (and recently occasional female violinists for live work) ever since.
 * In its nearly 40-year history, Journey has chewed up and spit out six lead vocalists, six drummers, three keyboardists, and three bassists, with several of those revolving door personnel lasting less than a year. The only person who has been ever-present since the band's founding in 1973 is lead guitarist Neal Schon, although keyboardist Jonathan Cain has also been a constant since 1980.
 * The Little River Band has replaced all of its members multiple times. In fact, the original lineup got in legal trouble in the mid-2000s when they wanted to tour under the name "Little River Band" and the current lineup wouldn't let them.
 * Thin Lizzy. The only constant members were Phil Lynott (vocals, bass and songwriting) and Brian Downey (drums). After Phil Lynott died in 1986, who will be touring under the name next time it appears is anyone's guess, but if you're lucky it'll at least have one of the members that were in the band whilst Phil was alive (since 1991 that's usually Scott Gorham). Ex-members include Gary Moore, Snowy White and Midge Ure. Their door revolved so much the issue has its own page on The Other Wiki.
 * Sloan subverts this: they regularly change who plays which instruments--even during concerts. However, the members have always been Chris Murphy, Patrick Pentland, Jay Ferguson, and Andrew Scott.
 * The Melvins have had a serious problem with keeping a bassist. While the two founding members have been around since the band's inception they have gone through six official bassists and multiple stand-ins/auditions. Kurt Cobain even auditioned but was rejected because he got so nervous he forgot all of their songs.
 * Hawkwind. They've had about 8 bassists, 8 keyboardists and 8 drummers, and they've gone from 7 members to 3 back up to 5 again, but always revolving around co-founder Dave Brock.
 * Rainbow were notorious for frequent changes during their lifetime; founder and only constant member Ritchie Blackmore never retained the same line-up for two successive studio albums. On one occasion he hired and then fired a bassist before he even got the chance to record on the album they were working on!
 * The Alan Parsons Project, centering around songwriters Parsons (also producer/engineer) and Eric Woolfson while the musicians rotated regularly. Woolfson sang and played piano from time to time; Parsons almost never sang (he talked through a digital vocoder on their first album).
 * Seminal death-rock group Christian Death has had 49 different members in the past 30 years; they're not a big band, mind you, they only ever have 4-5 people in the band at a time. They just rotate in and out like mad. They sort of have a Face of the Band, but it's changed hands several times: Rozz Williams, Valor Kand, Rozz Williams again, Valor Kand again.
 * Industrial rock group, Pigface, has had a total of 72 different members since its founding.
 * The only member of Queens of the Stone Age that has appeared on all their albums is its founder, Josh Homme. Homme's side project, Desert Sessions, is the same way.
 * Whitesnake were infamous for their constant personnel changes during the mid-80s. Infamously, David Coverdale fired all his band members who played on their best-selling album Whitesnake after the album's sessions finished, even though they had only played on that album. The current post-2003 lineup enjoyed relative stability for a while but in 2010 not one, not two, but THREE members left. The Other Wiki has a page dedicated to the various Whitesnake line-ups over the years.
 * Folk rock band Fairport Convention has had almost 30 members. None have been with the band for its entire 40-year career, and only a couple have been members for more than half of its existence. Several people were members for less than a year. Even the band's only more-or-less constant member, guitarist Simon Nicol, left the band for a period (1971 to 1976) before returning.
 * After drummer/singer Aaron Gillespie left in 2010, there are now no original members left in the Christian metalcore band Underoath. Between 1999 and 2003, every original member except for Gillespie quit the band.
 * ACDC was founded in 1973. Five years later, they were on their second vocalist, seventh bassist, and eighth drummer. The Young Brothers (Angus and Malcolm) are the only original members left.
 * Wings, Paul McCartney's second band, lasted for about eight years. During this time, they had five or six line-ups, three lead guitarists, four drummers (five if you count Paul when there were only three members), and two periods when only the core trio was present.
 * Guns N' Roses took its name partially from lead guitarist Tracii Guns, who was replaced in its first few months. The revolving door of guitarists, bassists and drummers accelerated after Axl took complete control. However, both of the band's keyboardists have remained ever since joining.
 * Black Sabbath have never recorded consecutive albums with the same lineup since Ronnie James Dio left the band in 1982.
 * Lynyrd Skynyrd are down to just one original member, lead guitarist Gary Rossington, due to the deaths, retirements and/or departures of various original and classic lineup members in the 1990's and 2000's. Not only that, but Rossington is the only member of the current lineup that played with the band before their 1977 disbanding.
 * Jefferson Airplane/Jefferson Starship. Just look at this list. Dear god.
 * The Smashing Pumpkins, both incarnations (the original and the reunited).
 * The same goes for The Yardbirds. In both the original band and the current reformation, Chris Dreja and Jim McCarty have been the only consistent members.
 * Nine Inch Nails, at least as a touring band. Trent Reznor employed 19 different musicians across eight major touring cycles, often as a four-piece band.
 * Faith No More went through a flurry of lineup changes in the early to mid 80s, then replaced the lead singer with a skinny kid from another band and stayed constant for a few years. Cue a quick series of guitarists before the breakup. Since the reformation in 2009, they've kept the same lineup from their last studio album in 1997.
 * The Doobie Brothers are so notorious for this, they inspired this pun; "She's had more members in her than the Doobie Brothers!"
 * There are two categories of Sound Horizon band members: Revo and people who aren't Revo.
 * Prog/Pomp rock band The Enid have had numerous changes of lineup since their formation in 1975, with only keyboardist/composer Robert John Godfrey being common to all.
 * Dave Grohl admits that he was afraid the Foo Fighters were becoming this. (all the first four albums have different line-ups and two bandmembers didn't even play in any of those - William Goldsmith had his drum tracks on The Colour and the Shape replaced with Grohl's ones, and guitarist Franz Stahl left after the tour for that album was finished) But since then, the only change has been an extra member.
 * Christian Rock band Petra was like this throughout its career, in particular during the 80's. Rarely did two consecutive albums have the same lineup.
 * The Cure has had 12 members since 1976, but the only consistent member has been lead singer Robert Smith.
 * What, still no mention of Fleetwood Mac?
 * The Byrds from 1966 to 1969. Roger McGuinn was all that remained of the original group throughout its tenure.

Rhythm & Blues

 * Tower Of Power. They've been together for 43 years, and have had at least 60 members.

Ska

 * No Doubt up until 1995.

Unsorted

 * The Temptations
 * The Crüxshadows. Except for lead singer/front man Rogue, nobody's been around since the beginning.
 * Da Yoopers, a comedy band from Michigan. They were founded in 1975 and only lead singer Jim DeCaire and keyboardist Lynn Anderson (no, not the lady who sang "I Never Promised You a Rose Garden") are original. What's more, all of their albums from the second onward have included large numbers of "unofficial" members.
 * Godspeed You! Black Emperor started out as a trio, then ballooned to about 15 members before settling down to 8 or 9 from then on.
 * The Hit Crew, a "band" used for all the Drew's Famous CDs that are ubiquitous at party supply and drug stores. They cover every musical genre, and some of the CDs are quite good (and others are terrible). Every single one is attributed to "The Hit Crew" - from New Age to Disco to Metal to Country. The lineup is different from album to album and even song to song.
 * Rasputina - after going through innumerable lineup changes, some of which lasted for several years at a time, founder Melora Creager is the only original member left and the only member to appear on every album.
 * Lords of Acid has turned into this as of its most recent (2012) lineup -- Praga Khan is the only member of the original left (he's credited as "Head Perv"), and DJ Mea is something like the band's fifth female lead singer.

Fictional bands

 * In Mystery Science Theater 3000: Eegah Joel and the 'bots draw attention the unnamed surf-rock band that switched lead guitarists twice in the middle of a single song.
 * Spinal Tap, when it came to drummers.
 * Based on Saxon's inability to keep a drummer.
 * Very minor example, but apparently, Octavia's band in My Little Pony Friendship Is Magic.