Adventure Duo

A specific Hero/Lancer pair common to adventure games. The Hero tends to be fairly serious, at least for what world they're in. They usually retain a sarcastic sense of humour and are quite literal-minded. The Lancer, on the other hand, is weird. They might be neurotic, borderline psychotic (or they are psychotic), naïve, cowardly, lecherous, treacherous, whatever. They might occasionally act serious when the plot demands, but in gameplay they're an oddball.

The reason for this is so that when The Hero points something out, The Lancer will make a comment about it which is funny, helping the player to remember the clue.

Like Salt and Pepper, but without the racial element. Often confused with Battle Couple, which is entirely different. Usually.

Examples of Adventure Duo include:

Anime and Manga

Villain Example: Straight Man Kakuzu and Ax Crazy Hidan in Naruto.
Sakura and Kero from Cardcaptor Sakura.

Comic Books

Cable and Deadpool, with a heaping (and frequently Lampshaded) side order of Ho Yay.
Havok and Polaris, from the first volume of X-Factor. Havok wrings his hands so much over the responsibility of leadership that Polaris has to gently remind him to not be so much like his brother Cyclops. Polaris has deep-seated insecurities that crop up occasionally, so they have been known to swap roles.

Film

Miss Bianca (hero) and Bernard (sidekick) in The Rescuers.
Pedro and Nico from Rio. Basically Timone and Pumbaa as birds.

Live-Action TV

Mal and Zoe of Firefly somewhat invert this, where Zoe is the cool, levelheaded and serious one, while Mal is the somewhat weird one despite being the lead character.
The same thing is done in Farscape, where Aeryn is so in control that she's only ever out of control for one or two scenes in the entire series, and John starts out spooked by all the alien life and gets progressively crazier as it progresses. Also a Battle Couple.
House and Wilson.
Supernatural: Sam and Dean Winchester. Played straight in Sam-centric episodes where the more serious Sam is The Hero and Dean is The Lancer. Inverted in Dean-centric where the goofier (but very broken) Dean is The Hero and Sam is The Lancer.
Keen Eddie had Eddie and Monty.

Video Games

Phoenix Wright: Ace Attorney has Phoenix Wright (sarcastic, literal hero) and Maya Fey (happy-go-lucky oddball). Eventually he encounters Pearl who is less odd, but only because she's a little girl - her personality is equally upbeat, but more bolshy than Maya. And Maya's Suspiciously Similar Substitute, Ema, is even more happy-go-lucky and even more naive.
- And when Franziska von Karma, the very serious, whip-happy prosecutor, tags along with you in the third game, her general misunderstanding of American/Japanese culture and many things outside her area of expertise lead to much the same effect as if she was Maya.
- And it's taken pretty much to the extreme with ultra-sarcastic, refined Edgeworth and his sidekick Gumshoe, who's like Doctor Zoidberg without the lobster.
  - Edgeworth gets Multiple sidekicks throughout his own game. Gumshoe and Franziska are the only returning characters to fill this role while the most prominent of the new characters is Kay Faraday, a self proclaimed Great Thief. 2 different stewardess take the role as well during the second case as you are on a plane mid-flight. There's also 13 year old Franziska and new cop Gumshoe who are paired with Edgeworth during a flashback case while he still strived for perfection leading to a slightly diffrent feeling then their present day selves. Also Franziska is the butt of many short jokes during this time
  - Although this relationship is inverted in Apollo Justice: Ace Attorney, where Ema is now substituting for Gumshoe, and shows open disdain for new prosecuting attorney Klavier, who she describes repeatedly as a "glimmerous fop".
  - Apollo does get Trucy, though.
- "Bolshy"?
Neverwinter Nights 2 has the (hopefully) more levelheaded player character and Khelgar, the psychotic dwarf.
- Though the game has many possibilities, especially adding in Mask of the Betrayer. You can play the silly one with Elanee, Casavir, Safiya, Kaelyn, or Okku as the serious sidekick; or you can play the serious member of the pair with Bishop, Khelgar, Neeshka, or Gann as the sillier sidekick.
Depending upon how you play it, the player character can be the silly one with Bastila as the overly serious counterpart in Knights of the Old Republic.
- A similar situation can occur with the player and the Handmaiden in the sequel.
Jade Empire has the potential for the player to be quite silly, with Silk Fox constantly reminding him/her of the seriousness of the situation. Black Whirlwind and that other guy who is with him when you first encounter them in the forest count too.
Dragon Age is set up so that the Warden is usually going to be the Only Sane Man while everyone else in your party, including Alistair and Morrigan who both come closest to playing The Lancer, are at least slightly mad.
The best example in Dragon Age 2 is inverted, with Silly!Hawke as the lead and Aveline as The Lancer.
- Aveline is the best at playing the Straight Man without even knowing it. Varric can do it too, but he knows it. For the rest you're going to have to step up for sanity sooner or later.
The Sam & Max: Freelance Police games has Sam the sarcastic, literal hero, and Max, who's... er, Max.
- Deconstructed in Sam and Max Season 3 Episode 4: Beyond The Alley Of The Dolls, when the Sam clones were made because Sam is 'the perfect straight man', meaning they could be easily controlled by a Funny Guy.
Baldur's Gate has Jaheira the wise fighter-druid, and Khalid her neurotic husband. Or Khalid the gentle and cautious fighter and Jaheira his overly willful wife. Make of that what you will. They're both just slightly weird.
- Depending on how you play the game the Player Character can have this relationship with several of the party members. Including his/her love interest.
Mario (hero) and Luigi (sidekick) in the Mario series when Luigi isn't simply a Palette Swap of his big brother or a "Player 2" option (for example: the Mario & Luigi games).
Banjo (hero) and Kazooie (sidekick) in the Banjo-Kazooie series.
Rayman (hero) and Globox (sidekick) in the Rayman series.
Jak (hero) and Daxter (sidekick) in the Jak and Daxter series.
Grim Fandango stars Manny Calavera, a driven, lovestruck Grim Reaper, and his sidekick Glottis, an eight-foot-tall gearhead demon with a gambling problem and a weakness for nitroglycerin martinis.
Ratchet and Clank also inverts this, with main character Ratchet being fun-loving and whimsy, and sidekick Clank being serious and out to save the galaxy.
From Pokémon Diamond and Pearl on, it appears that the player character of the opposite gender from the PC you choose is your "rival". He/She is more of just a friend than a rival, though.
The Legend of Spyro trilogy pairs the eponymous character up with Sparx the dragonfly, who compensates for being The Load in combat by having wisecracks for every situation.
- This behavior pattern makes it a Crowning Moment of Awesome when Sparx actually K.O.'s one of the more annoying bad guys with a single punch (granted said antagonist wasn't much bigger than Sparx himself, but it was still a cathartic moment).
Yooka and Laylee, from Yooka-Laylee.
Inverted in Snatcher. Gillian, the hero, is a Handsome Lech with an odd way of looking at the world, and Metal is a literal strait-laced snarky robot. However, most of the environmental observations are governed by Metal, and Gillian takes the helm in conversations where his oddness can really shine.
In Growlanser: Wayfarer of Time the protagonist, Crevaniel, travels with a quirky, fairy-like familiar.
Soul Nomad and The World Eaters has Revya, a Wide-Eyed Idealist Heroic Mime who wants to save the world, and Gig, the Heroic Sociopath Omnicidal Maniac who lives inside the former's head and wants to wantonly destroy, corrupt and befoul everything and generally make the world a worse place because he thinks it's funny, but has to come along on the world-saving anyhow and generally snarks about all the plot points and characters.
- This dynamic is a bit different in the Demon Path, in which both Revya and Gig are Omnicidal Maniacs and get on like a house on fire... Or a pair of insane maniacs who like setting fire to houses. And trees. And people. And everything else.
Neku and Beat in The World Ends With You, and Neku and Shiki to a lesser extent. Neku is always serious and sarcastic, while Beat is goofy, impulsive, and stubborn. Shiki tries to pretend to be always cheery, but it turns out that she's not exactly what she appears.
In the freeware adventure game Ben There, Dan That! Ben is the more straightforward hero, while Dan is a Cloudcuckoolander but is crazy good at video games.

Web Comics

The Order of the Stick provides us with Roy and Elan (at times, V, Durkon and occasionally Haley play the serious role, while Belkar also plays the goofy role). Also provides us with the villainous subversion: Xykon is the main villain, and just likes to goof around, while Redcloak is the serious one who makes all the plans and preparations. Strangely, the "goofy" one is the more powerful one.
- Xykon is mostly just bored, inability to sleep and can only spend so many hours working on artifacts, pose him with the problem of how to spend those remaining hours. Up until Xykon gets ticked off when Redcloak loses Xykon's Soul Jar when V attacked. Xykon then proceeds to become more serious.
8-Bit Theater provides us with Fighter who is a Cloudcuckoolander with a very literal take on things (metaphors don't exist for him), and Black Mage who is... all of The Lancer traits listed at the top of this page.
The title characters from Triangle and Robert.

Web Original

In The Gamers Alliance, there is a villainous variant with Kaizoku who is the snarking and mostly serious fairy pirate and Shuu who is his oddball kitsune companion in a human shape.

Western Animation

Adventure Time gives us Finn and Jake.
Phineas and Ferb.
Chip and Dale, in Chip 'n Dale Rescue Rangers more than anything, though sometimes in the cartoon shorts they first appeared in.
Yet another subversion is that of Bonkers, where the lead character is well, a toon, whereas his partner and arguable sidekick Lucky Piquel is generally more level headed.
Rudy and Penny from ChalkZone.
Jimmy and Beezy from Jimmy Two-Shoes.

Real Life

Josiah and Elanor Creasy, the Happily Married captain and navigator of the clipper Flying Cloud.
Samuel and Lady Florence Baker. Florence was abducted from Austria-Hungary and sold to a Turkish slave caravan. Samuel found her in a slave market in Vidin and fell in love with her. When he was outbid by the Pasha, he bribed the guards and ran off with her. The two were subsequently inseparable. They searched for the source of the Nile together, and discovered Lake Albert. Later in life they worked to put down the slave trade in Africa. It took them a while to get around to getting married, but they eventually did -- possibly twice, once in Bucharest (maybe; it's undocumented) and definitely once in England (which is well documented).