Jason Morgan Ritter (born February 17, 1980) is an American actor. The son of John Ritter and Nancy Morgan, he is known for his work in television series such as Joan of Arcadia (2003–2005), Gravity Falls (2012–2016), Another Period (2015–2018), Kevin (Probably) Saves the World (2017–2018), Raising Dion (2019–2022), and Matlock (2024–). For his portrayal of Mark Cyr on Parenthood (2010–2014), Ritter was nominated for the 2012 Primetime Emmy Award for Outstanding Guest Actor.

Ritter made his feature film debut in Mumford (1999). Subsequent credits include Swimfan (2002), Freddy vs. Jason (2003), Raise Your Voice (2004), Happy Endings (2005), The Education of Charlie Banks (2007), W. (2008), The Perfect Family (2011), Wild Canaries (2014), The Meddler (2015), Carrie Pilby (2016), Bitch (2017), The Tale (2018), and Frozen 2 (2019).

Ritter was born on February 17, 1980, in Los Angeles, California, to actors Nancy Morgan and John Ritter. He is a grandson of actors Tex Ritter, who died six years before Ritter was born, and Dorothy Fay. His stepmother is actress Amy Yasbeck. Ritter has three siblings, including actor Tyler Ritter.

Ritter's television debut happened during the opening credits of the sixth season for his father's sitcom Three's Company. Actress Joyce DeWitt recalls: "Our director, Dave Powers, was just shooting from the cuff when we would go on location to shoot the credits. There was a rough draft, but not really a game plan. And because we were going to be all day on location (at the Los Angeles Zoo in Griffith Park), people brought their children, their wives, whatever, it was kind of a group event, and Davey was just grabbing anybody and everyone to throw into those credits. In my credit, where I'm down and this little boy toddles in, that's Jason Ritter, John's first child."

He attended middle and high school at the Crossroads School in Santa Monica, California, alongside Simon Helberg, who became his roommate at NYU. Ritter attended and graduated from New York University's Tisch School of the Arts, where he studied at the Atlantic Theater Company. He later studied at the Royal Academy of Dramatic Art in London.

Ritter made his professional acting debut at age 10, playing Harry Neal Baum in the 1990 television film The Dreamer of Oz: The L. Frank Baum Story. Several years later, he had a supporting role as Martin Brockett in the 1999 film Mumford, a dramedy directed by Lawrence Kasdan.

Ritter's film work throughout the early 2000s included prominent parts in teen-oriented projects such as Swimfan (2002), Freddy vs. Jason (2003), and Raise Your Voice (2004). Between 2003 and 2005, he appeared as Kevin Girardi, the disabled brother of the titular main character, on the CBS family drama series Joan of Arcadia. Next, he played a young man struggling to come terms with his sexuality in the dark comedy Happy Endings (2005), with Stephen Hunter of The Washington Post commenting, "The acting in this ensemble is of such a high order that the movie simply takes you in and makes you feel these lives as real."

Ritter's portrayal of an Ivy League college student in The Education of Charlie Banks (2007) was met with critical acclaim: The Hollywood Reporter referred to it as a "head-turner" performance that combined "a believably brooding intensity with a bad boy swagger that brings to mind [a] young Matt Dillon."