Carried by the Host

A trope of Game Shows, Magazine Shows and similar. This is where the host or other regular "character" in such a show manages to add far more to a show than would be expected; expect a ton of Periphery Demographic in any show that manages to evoke this. Related to Ensemble Darkhorse, but separate as it tends to involve the closest things such shows have to a central character (although it can sometimes involve a side star).

If the star is replaced by someone else (even temporarily) expect invocations of Replacement Scrappy, They Changed It Now It Sucks, Ruined FOREVER and Fanon Discontinuity (as close as a nonfiction show can get anyway).

Game Shows

 * Cash Cab is literally driven by Ben Bailey.
 * Or Adam Growe in Canada
 * Roy Walker of Catchphrase. When he left the show, the show's popularity left with him and the new host found himself with a broken leg mere seconds into his first episode, the show itself was axed three years later.
 * Richard O'Brien on The Crystal Maze.
 * Deal or No Deal wouldn't be half as much fun without Howie Mandel. Or Noel Edmonds. Or Andrew O'Keefe.
 * Richard Dawson, and later Ray Combs, both were immensely popular hosts on Family Feud, and each brought a lot to the program. Louie Anderson, Richard Karn, John O'Hurley and Steve Harvey, on the other hand, provide excellent foils, as the show has never recaptured its former popularity with the four new hosts.
 * Robert Llewellyn on Junkyard Wars.
 * Knightmare features Hugo Myatt presenting in character as dungeon master Tregard.
 * Olmec of Legends of the Hidden Temple, much moreso than the actual (rather mediocre) MC, Kirk Fogg.
 * The '70s revival of Match Game was all over this trope, taking what could have been a boring parlor game and putting it into the hands of six celebrities and emcee Gene Rayburn, all of whom were much more interesting to watch with their antics than the actual game they were playing. Even better were episodes to be shown later in the week (apparently, the shows for a week were all shot on one day, and somewhere around Wednesday's show everyone took a lunch break... for the celebrity panel, there were often three, four or five martini lunch breaks, and it showed through the increasingly anarchic behavior of those installments...)
 * Marc Summers of Nickelodeon's Double Dare.
 * Possibly made more awesome because Summers suffered from Obsessive Compulsive Disorder and no one at the time would've guessed even though Double Dare was not what one would call a, erm, clean game show...
 * It was even worse with his later show What Would You Do? which was just as messy but had no set format. Furthermore in the last segment of the show (where they would put cards with various stunts on people's heads and they would have to either do the stunt or visit the various pie contraptions) they always gave Marc the the messiest thing they could think of. There's a reason why they usually ran out of time before they got to him...
 * Nickelodeon Guts wouldn't be the same without Mike O'Malley and Moira Quirk, and it really showed with My Family's Got GUTS, where Ben Lyons and Asha Kuerten replaced them. Though the former duo weren't working for Nickelodeon at the time, and Asha was praised by some fans for equalling Moira.
 * No one but Peter Tomarken could host Press Your Luck, as Todd Newton painfully demonstrated with Whammy!
 * Peter Tomarken almost hosted Whammy!. GSN filmed two pilots: one featuring Peter Tomarken and the other featuring Todd Newton. Just think about What Could Have Been.
 * The Price Is Right.
 * Jenny McCarthy and Singled Out. The show only lasted a season and a half after her departure, despite being replaced by Carmen Electra.$
 * Takeshis Castle. Watching people falling in mud and injuring themselves: funny. Watching them do it to Craig Charles' commentary: hysterical.$$
 * ABC's Wipeout (Not to be confused with Peter Tomarken's much older show of the same name): John Henson and John Anderson's commentary is as funny as watching the contestants trip and fall.
 * Total Wipeout (the UK version, airing on BBC) itself may count too. It's hosted by Richard Hammond, and his snark makes watching the contestants fail miserably even funnier.
 * The Swedish Wipeout also would be nowhere as good without its hilarious hosts.
 * In Australia, there was practically a national outcry (among people of a certain age group, anyway) when "Baby" John Burgess was dropped as host of Wheel of Fortune.
 * Regis Philbin for Who Wants to Be A Millionaire?
 * Also applies to the German version. The host, Günther Jauch, is probably the most popular person in this country.
 * Win Ben Steins Money was carried by the father/son-like relationship between Ben Stein and Jimmy Kimmel. When Kimmel left, it went downhill in a hurry.
 * No one ever, ever, tuned into the original You Bet Your Life for game value.
 * Just about any show hosted by Bill Cullen that wasn't the original Price is Right. Most of the shows he was associated with went off the air in a year or less (Winning Streak, Hot Potato, Child's Play, etc.) but he was such a phenomenal host that he made even the most mediocre game format watchable.
 * To be fair, though, many of those shows he hosted that did end up failing generally ended up doing so as a result of getting Screwed By the Network, not because of any formatting flaws.
 * For most people, Jeopardy just wouldn't be the same without Alex Trebek (at least since it was Un Canceled in The Eighties).
 * The NBC version of The Singing Bee had some mediocre success with host Joey Fatone. However, when the show channel hopped to CMT, they hired stand up comic Melissa Peterman. It's been more successful, notably since Peterman's charisma is able to cover when a contestant is nervous, too quiet, or simply dull.

Panel Shows

 * Angus Deayton, the original chairman of Have I Got News for You, remains popular among fans of the show, several years after being sacked for personal indiscretions. While the rotating guest hosts have produced many popular replacements, there is still a considerable segment that wants Angus back full time.
 * Meanwhile, it's nigh impossible to imagine the show without Ian Hislop (who's never missed an episode) or Paul Merton (who took the eleventh series off and has noted, as have others, that the show picked up somewhat after that little experiment).
 * Humphrey Lyttelton was I'm Sorry I Haven't a Clue to such an extent that his death in 2008 and subsequent replacement by Stephen Fry, Rob Brydon and Jack Dee has elicited all of the complaints listed above. It's still good, but it's definitely not the same.
 * Nicholas Parsons, host of Just a Minute, and now the last surviving original participant. Over the years, the show has seen many, many different panellists and their personal styles, but they've all made fun of the chairman, and he's always Lampshaded it.
 * Simon Amstell and/or team captains Phil Jupitus and Bill Bailey on Never Mind The Buzzcocks.
 * Being put to the test now that Amstell and Bailey have both left the show.
 * Ten years ago, it was being carried by Jupitus, Mark Lamaar and Sean Hughes, and the thought of continuing once Lamaar and Hughes left provoked the same reaction.
 * Talkin Bout Your Generation wouldn't be half as fun without Shaun Micallef. What would normally be a bland family-oriented quiz show ends up hilarious due to the Shaun's Post Modern Pythonesque insanity.

Reality Shows

 * The Amazing Race just wouldn't be same without Phil Keoghan.
 * Viewing of American Idol dropped drastically every time judges were replaced. With Simon gone and now running the American version of X-Factor, it is a safe bet Idol isn't long for life.
 * Anderson Cooper on the first two seasons of The Mole. He was by far one of the funniest and most charming game show/reality show hosts out there.
 * Jeff Probst is this for Survivor. For a show that loses many viewers each season due to having too similar concepts each season, many people continue watching it partly because of Probst.
 * Swedish Expedition: Robinson (the original Survivor) has gotten this in Paolo Roberto, who took over as host in 2009. Roberto's no-nonsense attitude (like when he chews one tribe out and basically calls them morons for not having learned how to make fire before going on the show) has quickly become a favorite for most viewers, as has his various quirks such as the way he bellows "Köööööööööööööööööör" (means "go") to signal the start of any competition.
 * Well, the guy did beat the crap out of a seven foot behemoth who's immune to pain.

Miscellaneous

 * Bob Saget on Americas Funniest Home Videos (though they try to make it seem like Tom Bergeron was always there these days...)
 * Dominic Diamond on Games Master (also notable for Season 3 being considered along the lines of Canon Dis Continuity for him being replaced by Dexter Fletcher for that season).
 * Both the Japanese and American incarnations of Iron Chef, with Chairman Kaga and the Japanese commentators/Alton Brown respectively. Gordon Elliott (in the IC Japan New York special) and William Shatner (the doomed Iron Chef USA) have both tried to fill the hosts roles with poor results.
 * While Iron Chef USA was awful Shatner himself as Chairman was thoroughly awesome.
 * Myth Busters owes most of its success to the dynamic duo that is Adam Savage and Jamie Hyneman. (The Power Trio of the Build Team have their own unique personalities that are also interesting to watch.) The short-lived show "Smash Lab" tried to replicate the explosions and large-scale experiments similar to Myth Busters, but failed because the hosts weren't nearly as entertaining when constructing the giant engineering project of the week.
 * The two shows had a fundemental difference as well: Myth Busters was about trying to prove or disprove a myth, while Smash Lab was mostly about creating solutions in search of problems.
 * A show that manages to get it right, but not quite as perfect as Myth Busters is Time Warp as the two hosts actually knew the science behind most of what they were talking about and also had interesting personalities to help keep viewers from getting bored.
 * Interestingly, the Myth Busters were originally encouraged to emulate the onscreen dynamics of another popular Discovery Channel show, American Chopper (itself a prime example of this trope; the show has long since been more about family drama than anything to do with motorcycles). They eventually refused to keep acting this way, and their popularity has only waxed since.
 * Joel McHale of The Soup.
 * Tom from Cartoon Network's Toonami. When he was replaced with TOM 4, you just know Toonami's in trouble.
 * Jeremy Clarkson, James May, and Richard Hammond on Top Gear. And The Stig, of course. Both Clarkson and May presented Old Top Gear before it was canceled, though not at the same time.
 * Unsolved Mysteries was never the same without Robert Stack.