Neil Flynn grew up acting in school plays. He has been awarded with two Jefferson Awards for excellence in Chicago Theatre. Later on he became involved in projects on both the big and small screen.
Flynn has had roles in several features, among them The Fugitive, Magnolia, Mean Girls, Chain Reaction, and more. Flynn's role on Scrubs as The Janitor became so pivotal during the first season that his guest star position was upgraded to resident cast member. Flynn is a master at improvisation and usually makes up his lines on the spot.
In the first episode of the series J.D. sees The Janitor fixing a sliding door that is stuck, and he suggests it might have been caused by someone who stuck a penny in the door. The Janitor thinks that person is J.D. and forms a grudge against him.
Initially it was believed that The Janitor was a figment of J.D.'s imagination because for a long time he was the only one who interacted with him.
The Janitor often comes up with new ways of tormenting J.D. Some of his practical jokes have been on the severe side, such as destroying J.D.'s bike, trapping him in a water tower and stranding him in the middle of nowhere.