Liam McPoyle is a member of the McPoyle family.
Throughout the series, it is implied that Liam is in an incestuous relationship with his brother, Ryan and sister, Margaret. It is also demonstrated that he likes to watch his siblings have sex with other people. Like his siblings, Liam likes to crank the heat so he is constantly sweaty. His attire of choice is underwear and a bathrobe. His favorite drink is milk. The McPoyles have a complicated relationship with the gang, usually as enemies, but are occasionally shown to be more friendly and socializing at the bar ("Charlie Got Molested", "Who Got Dee Pregnant?").
Liam is notable for sudden outbursts of tone and volume in his diction. He typically speaks with a lazy, laconic mumble, but is known for his violently impulsive comments about issues in which he is passionate and angry.
Liam seems to favor "fist bumps" as a sign of solidarity or friendship, but only offers a limp-wristed fist to his counter-parts (usually Charlie), followed by the insistence that they "bump it".
Liam and Ryan accused Coach Murray of sexually molesting them when they were in elementary school. Upon hearing this news, Charlie grew concerned and visited the McPoyle's apartment. There, he told them he knew they were faking, but they threatened to turn him in as the ring leader if he didn't go along. They watching his mother hold an intervention for him, but Charlie later ratted them out to the police, who had them arrested. ("Charlie Got Molested")
- Season One: "Charlie Got Molested"
- Season Two: "Charlie Goes America All Over Everybody's Ass"
- Season Three: "The Gang Gets Invincible", "The Gang Gets Held Hostage"
- Season Six: "Who Got Dee Pregnant?"
- Season Eight: "The Maureen Ponderosa Wedding Massacre"
- Season Nine: "The Gang Squashes Their Beefs"
- It’s Always Sunny: Gang Goes Mobile
- Liam is a left-hander. ("The Maureen Ponderosa Wedding Massacre")