Part of a show-business family, Einstein's comedic resume included playing the fictional daredevil Super Dave Osborne, and, most recently, the dour Marty Funkhouser on David's HBO series.
His brother, writer, director and actor Albert Brooks, remembered Einstein on Twitter as "a great brother" and "a brilliantly funny man."
David, through HBO, issued a statement that said, "Never have I seen an actor enjoy a role the way Bob did playing 'Marty Funkhouser' on 'Curb.' It was an amazing, unforgettable experience knowing and working with him. There was no one like him, as he told us again and again. We're all in a state of shock."
Einstein's parents were both performers. His mother, Thelma Leeds, was an actress, and his father, Harry Einstein, a comic. (Brooks changed his name, joking about having been originally saddled with the name "Albert Einstein.")
Einstein was a master of deadpan comedy, having originally started writing and playing the character "Officer Judy" on the "Smothers Brothers" show, which was known for its irreverence and canceled by CBS in 1969.
Einstein went on to write for various TV programs -- including "The Sonny and Cher Comedy Hour" -- before creating Super Dave, appearing as the character on the sketch comedy show "Bizarre," on Johnny Carson and David Letterman's late-night shows, and later playing him on his own Showtime series and in an animated sitcom.
In addition to his recurring role on "Curb" -- which lasted from 2004 through its most recent season -- Einstein appeared in numerous TV shows and movies, including his brother's film "Modern Romance" and "Ocean's Thirteen."