Here's a bit of trivia I learned from Seinfeldia-- The first time the character Frank Costanza appeared on the sitcom, he was played by another actor (John Randolph). Randolph was replaced by Jerry Stiller. For continuity's sake, they reshot the Randolph scene with Jerry Stiller for the reruns that were distributed for syndication.
Here is Randolph. I don't remember ever seeing this version before.
And here is a memorable Jerry Stiller scene.