Over the course of nine seasons and 180 episodes, Seinfeld became one of the shows that defined the 1990s. It also left an indelible mark on television comedy in the wake of its controversial finale in May of 1998. Sadly, since Seinfeld has been off the air for decades now, we've lost a number of Jerry and company's old friends and nemeses in real life. Don't you just hate being out of the loop? Here are the Seinfeld actors you may not know passed away.