Muscle Dad Sorenstein is Muscle Man's deceased father. He appeared in "Trucker Hall of Fame". He was perceived to be a trucker, but was actually a forklift operator, telling his son he was a trucker so he would be proud of him. He loved to prank truckers, random people, and even Muscle Man himself. Mordecai, Rigby, and Muscle Man call him "Muscle Dad." He died after he got mauled for putting a cactus under a cop in a bear costume who was actually a real bear. He later returned in the episode as a ghost, making amends with his son. He also made an appearance in "Power Tower" in order to congratulate his son for winning the Biceptennial.