Mark O'Keefe is an American screenwriter, who specializes in the comedy genre.
His brothers are Broadway and movie songwriter Laurence O'Keefe (also called Larry) (composer and lyricist of shows including Bat Boy: The Musical and Legally Blonde) and Seinfeld writer and producer Dan O'Keefe (also called Danny).
Their father, Daniel O'Keefe Sr., invented their private family holiday Festivus, which gained national exposure when depicted in an episode of Seinfeld (written by Danny), and which is now celebrated across the globe.
The show, starring Judge Reinhold, was on The WB in the summer of 2003, but only 5 episodes aired before it was cancelled.
The show generated controversy among people who felt that it depicted homeschooling in a negative light.