Mr. Treeger was the building superintendent at Monica, Rachel, Joey, and Chandler's apartment building. His first appearance is in "The One Where Heckles Dies", when the friends are cleaning Mr Heckles' apartment. He later appears in the second season holiday episode when Monica and Rachel's knob on the heater breaks off, causing their apartment to get very hot. He also appears in season 4, "The One With The Ballroom Dancing", where Joey gets Rachel into trouble with him and he threatens to throw Monica and Rachel out of their apartment for illegal subletting (a fact made clear many times throughout the series, as Monica took control of and subletted the spare room of the apartment and continued living there even after her grandmother, the real lessor, passed away). In order to avoid this, Joey agrees to help Treeger to practice his ballroom dancing to impress a lady-friend. He later appears in "The One With The Free Porn", where he tells Joey and Chandler about the time he got free porn on his tv and made the mistake of turning it off. Treeger's final appearance is in "The One Where Rachel Tells..." where he calls the fire department to break down the door to Chandler and Monica's apartment. It is also revealed that he attends yoga class with Ross. Although Treeger is mentioned, he does not appear in the final episode. In "The Last One", Monica told the gang to leave their keys for Treeger. He is the last character to be mentioned by name.
Hagerty also portrayed one other character on the show. This was a "grip" working on the movie in "The One With Joey's Big Break". In this episode, he hands Joey a bunch of balloons delivered to him from New York, together with a note saying "Congratulations on your big break" from Chandler as an apology for not believing in his independent movie.