Estelle Harris, the charming and combustible actor most famous for her role as Estelle Costanza on Seinfeld, passed away April 2 of natural causes. She'll be missed by TV fans everywhere, but she left behind an indelible legacy on the NBC sitcom. As Mrs. Costanza, George's overbearing, unsmiling mother, Harris created a hilarious portrait of a parent's perpetual disappointment — one that also rings true.