Jimmi Simpson is an American actor born on November 21, 1975, in Hackettstown, New Jersey, USA. He is known for his work across film, television, and theatre, earning nominations for BAFTA, Primetime Emmy, and Screen Actors Guild Awards.

He made his film debut in Loser (2000) and later appeared in Herbie: Fully Loaded (2005), Zodiac (2007), Date Night (2010), Abraham Lincoln: Vampire Hunter (2012), White House Down (2013), Under the Silver Lake (2018), and Unhinged (2020). On television, he played Liam McPoyle in It's Always Sunny in Philadelphia (2005–2023) and had roles in Psych, Breakout Kings, The Newsroom, House of Cards, Hap and Leonard, Westworld, Black Mirror, Unsolved, Perpetual Grace, LTD, The Man Who Fell to Earth, Pachinko, and Dark Matter.

On stage, he starred as Philo Farnsworth in The Farnsworth Invention (Broadway, 2007–2008), earning a Theatre World Award. He studied theater at Bloomsburg University and trained at the Williamstown Theatre Festival.