Dan Gillick is a man who was a temporary don while Fat Tony was serving jury duty. He was the accountant of Fat Tony's group and was a friend of Homer. He joined the Pin Pals to replace Otto, who was suffering a psychotic breakdown at the time.
As stated before, Dan was the accountant for the mafia, until he was temporarily a mob boss for Fat Tony. Dan may also have a daughter, Cassidy Gillick, who was mentioned when Dan took a fake phone call to ask his daughter what she would do if he disappeared.
Dan originally wears a light blue long sleeved shirt with a blue sweater vest. When he acts as temporary don, he wears a gray suit. When he was substituting for Otto, he was wearing the Pin Pals uniform.
At the first minutes of Penny-Wiseguys, Dan is showed as nervous and fearful of his associates such as Legs, Johnny Tightlips, Joey the Arsonist. Later in the episode, he grows a back-bone, yet grows more unstable and power hungry. Thankfully he grows aware of that, and begs Homer to stop him from possibly killing his associates.