Knuckles is the guardian of the Master Emerald, which is on Angel Island. Being gullible, Eggman tricked Knuckles into thinking Sonic and Tails Prower were going to steal the emerald. However, he found Eggman was really against him and joined with Sonic. Eggman had tricked him several more times after that, but Knuckles eventually found his way to the good side for good.
In Sonic Adventure 2, he fell in love with Rouge the Bat. However, he isn't in love with Rouge in the Archie Comics because of his relationship to Julie-Su in that universe.
He hangs out with a group called Knuckles' Chaotix, of which he is the leader. They are a varied bunch, consisting of Knuckles, Mighty the Armadillo, Espio the Chamelion, Charmy the Bee and Vector the Crocodile. They have starred in their own game, Knuckles' Chaotix.
He has appeared in the following games: