On "Seinfeld", which character invented the holiday Festivus?

On "Seinfeld," Frank Costanza is the character credited with inventing the holiday Festivus. In the series, George's father introduces Festivus as an alternative to the commercial pressures of Christmas.

Festivus is featured in the season-nine episode "The Strike," first broadcast in 1997. Frank explains that he created the holiday after becoming frustrated with the commercialism surrounding Christmas. His version includes an unadorned aluminum pole, a Festivus dinner, the airing of grievances, and feats of strength. The episode also supplies the memorable phrase "A Festivus for the rest of us."

There is an important real-world distinction. The O'Keefe family celebrated a private tradition called Festivus before the show: writer Dan O'Keefe adapted that family custom for "The Strike." So Frank Costanza invented Festivus within the fictional world of "Seinfeld," while Daniel O'Keefe originated the real-life tradition that inspired the episode.

Uncle Leo, Newman, and Cosmo Kramer did not invent it. Kramer helps bring Festivus into the episode's action, but Frank is the character who claims authorship of the holiday.