In Borderlands 2, deep in the Caustic Caverns, there is a ghost of a man sitting by a campfire that looks like he belongs in a different game. There is also a an NPC hanging around named Solitaire, which may or may not be a reference to Knight Solaire.

YouTube user Rofl316 was nice enough to upload some footage of the campfire. Check it out below.

Thanks to Danny Grim for the news tip!