|Family|| Mother: Nana
Father: Unnamed Father
Sister: Helen Seinfeld
Nephew: Jerry Seinfeld
Niece: Unnamed niece
Brother-in-law: Morty Seinfeld
|First Appearance||"The Pony Remark"|
|Last Appearance||"The Finale"|
|Portrayed By||Len Lesser|
When coming across Jerry, he exclaims, "Jerry! Hello!" with his arms wide open. He often brags about his son and his various accomplishments while working in the Parks Department. He, however, unintentionally became the leader of a different organization that did not like parks (episode 104). Leo's son is never seen but Jerry often refers to him as "cousin Jeffrey".
In the episode "The Pony Remark" Jerry reveals he doesn't like sitting next to Leo at dinner tables, because he grabs his arm while talking, "Probably because so many people have left in the middle of him talking." In one episode, Jerry Seinfeld unintentionally has Uncle Leo arrested for shoplifting at a local bookstore. During this episode, we learn that Uncle Leo has a record related to a "crime of passion". In another episode Leo receives a package for Jerry that Jerry seems to think looks suspicious. Jerry encourages Leo to open the package while talking on the phone and Jerry hears a loud explosion. However, Leo went unharmed, as a can of oven cleaner he left in the oven exploded, not the package.
In "The Finale, Part 2," Uncle Leo attends the trial of Jerry, Elaine, George, and Cosmo in Latham County. A deleted scene had him meeting Babs Kramer. After the four of them are found guilty, Uncle Leo was seen comforting Babs Kramer.