Lesser died Wednesday at the age of 88. In addition to playing Uncle Leo, Lesser, a character actor, appeared in TV shows like "Everybody Loves Raymond," "Gunsmoke," "The Munsters" and more.
Here are some of his classic Uncle Leo scenes from "Seinfeld."
Years after "Seinfeld" ended, Lesser talked about the fame the show brought him. Watch:
There's an outpouring of grief from "Seinfeld" fans on Twitter.
Sad day for all us Seinfeld fans, Uncle Leo has passed away--Len Lesser who played Leo died at 88 http://tiny.cc/ok5w8
@RandomDaveG A melancholy happy trails to Uncle Leo! He was a great man. Loved by many.
Goodbye Uncle Leo. Len Lesser, who played Uncle Leo on Seinfeld has died. He will be missed by all (even his son Jeffrey at the parks dept).
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