Who crucified Peter the Apostle upside down?

Roman Emperor Nero needed a convenient scapegoat to blame for the fire that destroyed large parts of Rome. He already found the Christians to be a major irritation so decided to blame the fire on them and began a persecution of followers of Christ. Peter, being a leader of the new religion, became a target of the insane Nero and he ordered him tortured and crucified. He felt that, by destroying the head of the Church, the religion would fall apart and disappear.