Seinfeld Easter Egg - Larry David Cameo

That is true - but Larry David also plays Frank Costanza's layer (non-speaking role). I can't remember which episode it is but it is at the beginning when Jerry and Elaine are walking down the street.

Yeah, it was the guy in the black cape. Jerry and Elaine argued "How wears a cape, Superman"

Larry David shows up fairly frequently. He was the voice of George Steinbrenner and, in one episode, played the physical part of Big Stein as well. He also provided a number of memorable off-camera voices including the "Is anybody here a Marine Biologist?!" guy and the "I ordered the Kosher meal." guy. He also appeared as one of the men in the Greenpiece boat with Russell Dalrymple in "The Pilot".

Somebody told me that Larry also played the bubble boy.

No, the bubble boy was played by Jon Heyman. BTW, George Costanza's high school teacher, the one with baked bean teeth who called George "Can't stand ya!" was named Mr. Heyman. Not a coincidence.

Larry David also played the voice of Newman the first time he was heard (he wasn't seen until later episodes). This was before Wayne Knight came aboard. The voice was later dubbed with Wayne's voice for repeats.

Frank Costanza's lawyer was a speaking part. At the very end of that episode, while the credits are rolling, he stops Elaine's friend from jumping off the bridge and introduces himself to her as "Frank Costanza's lawyer".

I think Larry David was also the guy on TV in that early episode where Jerry was dozing off watching TV. It was something scifi, don't remember the name, but it was him I'm pretty sure