Jason Jordan Segel (born January 18, 1980) is an American television and film actor, screenwriter and musician, known for his work with producer Judd Apatow on the short-lived television series Freaks and Geeks and Undeclared, the movies Forgetting Sarah Marshall, Knocked Up, and I Love You, Man, and also for his role as Marshall Eriksen in the CBS sitcom How I Met Your Mother.

Segel was born in Los Angeles, California, and raised in Pacific Palisades, California. Segel attended an Episcopal Church-affiliated school, though he was raised in his father's Jewish religion. Following the completion of elementary school, he completed his middle and high school studies at Harvard-Westlake School, where his 6'4" (193 cm) frame helped him as an active member of the state champion boys' basketball team. He was hoping to become an actor during his school days and acted in local theater productions at Palisades Playhouse.

He is known for his role as "Freak" Nick Andopolis on the short-lived NBC comedy-drama series Freaks and Geeks, about a group of suburban Detroit high school students circa 1980. He also personally wrote a song for his character, Nick, to sing to the lead female character, Lindsay (Linda Cardellini), in an episode of Freaks and Geeks. She and Segel dated for a few years following the show's cancellation. It was rumored that she dumped him for gaining twenty pounds, but it has since emerged that the statement was in fact a joke taken out of context.