Kip has been given two histories on Friends. In both he was Chandler's roommate before Joey. In "The One With The Dozen Lasagnas", Chandler tells Joey that Kip ran off and got married. Later, in "The One With The Kips", Rachel says that Kip and Monica dated and after they broke up, he was phased out. Although it is possible that he got phased out and then ran off and got married.
In "The One With The Blackout", Joey says that "Chandler's old roommate was Jewish".