Uncle Leo is a fictional character portrayed by Len Lesser in the American sitcom Seinfeld. He is Jerry Seinfeld's uncle. He made his debut in the second-season episode "The Pony Remark" and appeared in at least one episode in each of the additional seasons through the show's nine-season run. On the 25th anniversary of the show's debut, Rolling Stone ranked Uncle Leo as No. 6 on its list of "100 Best Seinfeld Characters," behind only Newman at No.