Jason Jordan Segel (born January 18, 1980) is an American actor. He is best known for his role as Marshall Eriksen in the CBS sitcom How I Met Your Mother from 2005 to 2014. He began his career with director and producer Judd Apatow on the television series Freaks and Geeks (1999–2000) and Undeclared (2001–2002) before gaining prominence for his leading roles in various successful comedy films in which he has starred, written, and produced.

Segel has starred in many comedic films such as Knocked Up (2007), Forgetting Sarah Marshall (2008), I Love You, Man (2009), Bad Teacher (2011), The Five-Year Engagement (2012), This Is 40 (2012), and Sex Tape (2014), as well as family films such as Despicable Me (2010), and The Muppets (2011). For his role as David Foster Wallace in The End of the Tour (2015) he received a nomination for the Independent Spirit Award for Best Male Lead. He also starred in the dramas Jeff, Who Lives at Home (2011), The Discovery (2017), Our Friend (2019), and Windfall (2022).

In 2023, he began starring as a therapist in the Apple TV+ series Shrinking, which he also co-created alongside Bill Lawrence and Brett Goldstein. For his performance he earned a Primetime Emmy Award for Outstanding Lead Actor in a Comedy Series nomination.