Ben Parker

From Spider-Man Wiki

Ben Parker was Peter Parker's uncle and looked after him after with Aunt May after his parents died. He was as loving as any uncle ever could be, but one day he was killed because his nephew gained powers used it for gaining money and didn't catch a thief when he could have. Ever since that day Peter Parker learned that with great power comes great responsibility.

[edit] Movie

In the recent Spider-man movies, it was revealed that it was the Sandman that killed him (even if it was an accident). The rest is unchanged from the comics. Uncle Ben said to Peter just hours before he died, "With great power comes great responsibility."