He's the best there is at what he does, and what he does is make gratuitous guest appearances.
Mike: Wolverine, or The Wolverine, is the second attempt to make a movie just about Wolverine. Except for the first three X-Men movies *snaps fingers*.
Jay: Oh snap! Oh no he di'int!
A Wolverine appearance? How novel. Seriously, this is the third time I've run into you this week, Logan.
—Iron Man, Runaways (written in 2005)
Matt Murdock: [Wolverine's] still an X-Man?
Steve Rogers: Yes.
Matt: And an Avenger?
Steve: When he can.
— New Avengers (written in 2005)
Wolverine: Hey, I'm an X-Man and on two Avengers teams.
Mockingbird: Yeah, how the hell do you do that?
Wolverine: Multi-tasking. It's my mutant power. Don't tell anyone.
—New Avengers (written in 2010)
Cyclops: All right men, you heard Beast: Jean has once again turned evil. So we're just going to have to kill her. Again. As usual we will split into teams: Team A will consist of myself, Emma, Colossus (who is also apparently back from the dead), Beast, and Wolverine. Team B will consist of Havok, Polaris, the other Xorn, Iceman, and Wolverine.
Wolverine: Uh, okay...?
Cyclops: Team C will consist of Storm, Psylocke, Jubilee will be on the team but not do or say anything, Bishop, Nightcrawler, and Wolverine.
Wolverine: Now wait just one minute here!
Cyclops: Team A will search the grounds to find and detain Phoenix. Team B will stay at the Mansion to fend off inevitable attacks from the Brotherhood. And Team C will go have adventures in Europe or something.
Wolverine: Wait up, eh! *pant pant pant pant* Whew!
Cyclops: Did you find Jean?
Wolverine: No, I just ran here from helping Team C in Europe!
Cyclops: Since when are you in the Avengers anyway, Wolverine?
Wolverine: I was getting bored only being on three teams while having my own solo adventures. Ya know a guy's gotta live a little!
[Wolverine]'s in EVERY BOOK. I think he just joined the JLA, and for some reason he's in the revised Penguin edition of Little Dorrit.
Rictor: Some unexpected showed up at the front door...you'll never guess who.
Wolfsbane Aw, God...
Shatterstar: Justin Bieber?
Rictor: No, it's not...
Rictor: Holy crap.
Wolfsbane: How did ye know?
Shatterstar: Well, he tends to be everywhere. Not at much as Justin Bieber, but still...