Role in Angelica Breaks a Leg
Because Dr. Dooser had trouble keeping track of Angelica's surname, as well as that of Antonio Peaches, a football player who really did have a broken leg, he had mixed-up their X-rays and believed that Angelica's leg was truly broken and Antonio's wasn't. He recommended keeping Angelica's leg in a cast, despite Didi's insistence that she and Stu find a second opinion from a different doctor (preferably one that was older and had more experience).
He appears again towards the end of the episode when he calls Stu and Didi to tell them that he had mixed up the X-rays and that Angelica's leg wasn't broken after all. He then hung up the phone and apologized for the mix-up to Antonio, who had injured his broken leg even more when he played in a football game.
U Can find Dr. Dooser gallery here.