Neil Flynn the actor that played The Janitor on scrubs was only supposed to be on the show for one season. But he was too funny a character to get rid of. He was so perfect for the role that in most of the scenes he was told to say and do whatever her wanted. No lines were written for him in most of his scenes.
It´s funny how Dr. Cox always makes fun of J.D. but then he is there for him when he needs him. Still, season 6 and on they didn't have too many moments. I hope when I finish the series that they actually become friends.