Uncle Leo is a fictional character portrayed by Len Lesser in the American sitcom Seinfeld.

On the 25th anniversary of the show's debut, Rolling Stone ranked Uncle Leo as number six on its list of "100 Best Seinfeld Characters," behind only Newman at number five and the four main characters: Jerry, Kramer, Elaine, and George.

[1] Uncle Leo is the brother of Jerry's mother, Helen; his last name is never revealed.

[3] When talking to people, Uncle Leo has a tendency to grab the person's arm (often uncomfortably) and hold them close.

Uncle Leo often brags about his son (Jerry's cousin Jeffrey, who never appears on the show) and his various accomplishments while working in the Parks Department.

His wife, Stella, is seen in the third-season episode "The Pen", but by the seventh season, he is either widowed or divorced.

Lydia found Jerry's comments funny, so Uncle Leo accused her of being an anti-Semite, as well.

This happens over the phone, and Jerry hears a loud explosion once Leo agrees to open the box.

Elaine later quickly draws new eyebrows on him with her eyeliner, leaving him with a comical expression of anger.

The episode reveals that Uncle Leo has a criminal record related to a "crime of passion".