Benjamin Parker, also known as Uncle Ben was Peter Parker's parent and guardian.
He was killed by a robber that Peter could had stopped. With Uncle Ben dead Peter learned that with great power, also comes great responsibility.
Uncle Ben was very protective of Peter, going as far as fighting some of the bullies that tormented young Peter. Peter became friends with Charlie Weiderman in high school, a teen even more unpopular than he was.
However, Charlie often provoked the trouble with the other teens. One day, he was chased to the Parker home by a group of bullies, led by Flash Thompson, and Ben intervened. Ben told them that if they wanted Charlie, they would have to go through him. Flash tried to, but was surprised by Ben's army training. As soon as the bullies were gone, he told the boy that he wasn't welcome at the house or with Peter.
In high school, a radioactive spider bite gave Peter spider powers. Creating the costumed identity of Spider-Man for himself, Peter sought first to exploit his newfound powers as a masked wrestler and then as a television star. Coming from a television appearance, Spider-Man saw a burglar being chased by a security guard. The guard called for Spider-Man to stop the thief, but Peter refused on the grounds that catching criminals was "not his job" since the dealer did not pay him the money. The robber got away.
A few weeks later, when Peter returned home from a Spider-Man show he was out on, he was informed that his beloved Uncle Ben had been killed by a burglar. Outraged, he donned his Spider-Man costume and captured the man only to realize to his horror that it was the same burglar whom he could have effortlessly captured earlier at the studio.
As a result, Peter considered himself morally responsible for Ben's death and resolved to fight crime as a superhero, and vowed never to let another innocent person come to harm if he could help it.