Muscle Man

Muscle Man, his real name Mitch Sorenstein, is one of the groundskeepers at the park. He is almost always seen hanging out with High-Five Ghost, as they get assigned jobs together by Benson. Neither Muscle Man nor High Five Ghost seem to live in Pops's house; in Rage Against the TV, it is shown that Muscle Man lives in a trailer with High Five Ghost. Muscle Man is a fan of Fist Pump, along with Rigby.

Personality and Traits
He also has a habit of taking his shirt off and twirling/throwing it. He appears to have a party type personality and enjoys "getting naked" as seen in Free Cake. When he is sad Muscle man eats protein powder with a spoon for comfort food as seen in Muscle Woman when he is crying and busy "stuffing his facehole" It is shown that Muscle Man sometimes does tend to annoy Benson and feels great about it, as seen in Don. He frequently uses the term "My mom!" as a response, which tends to make Benson very angry. He seems to be one of the minor groundskeepers, only in his 30s or late 20s. However, despite Muscle Man's annoying personality, he is highly trusted by Benson, even though he and High-Five Ghost tend to slack off more than Mordecai and Rigby do. It is revealed he has a brother and an uncle. Muscle Man mistakes Mordecai and Rigby for making fun of his mom. Though, he was probably kidding about thinking Mordecai and Rigby hated his mom.

High-Five Ghost
High-Five Ghost is to Muscle Man as Rigby is to Mordecai. They are usually seen together in the episodes. He usually gives a high five right after Muscle Man says a "My Mom" joke. In "My Mom", the two seem to slack-off as much as Mordecai and Rigby, if not more so. High-Five Ghost is Muscle Man's best friend.

Mordecai
Out of the two main characters, Mordecai seems to dislike Muscle Man more. He is annoyed by the constant "My Mom" jokes and even confronts Muscle Man about it in My Mom. Besides that episode, there is not much interaction. Muscle Man does throw his shirt at Mordecai in "Caffeinated Concert Tickets", but that may have been an accident rather than a direct confrontation. In the episode Muscle Woman, Mordecai successfully gets Muscle Man out of his sadness, and back with Starla. He may have been doing this just so that they would not have to do his work. Earlier in the episode, Mordecai tries to help Muscle Man by telling him to talk about his problems and feelings, but Muscle Man rejects him.Mordecai is awesome and Rigby sucks.

Rigby
Out of the two main characters, Rigby seems to like Muscle Man. Rigby likes to hang out with him during "My Mom", and seems to get along with him very well, yelling " Ohhhhhh!" along with him at the taco truck. They do have some confrontations though. In "Meat Your Maker", he goes to say Muscle Man pushed him at a party ( though Mordecai quickly says Muscle Man was not even there). Also by the end of "My Mom", Rigby goes on to say how he hates Muscle Man. Also in "Death Punchies", Muscle Man is forced to be look out, causing his eyes to burn. In the episode Muscle Woman, Rigby comes up with a plan to get Muscle Man and Starla back together. This may have been to get Muscle Man out of his depression, or just so that Muscle Man would keep working.

Benson
Benson trusts Muscle Man more than Rigby and Mordecai, as established in Appreciation Day, My Mom, and Muscle Woman. He does fire Muscle Man though in Don, but this may be due to the stressful situation that Benson was in. Benson also seems to understand Muscle Man and his antics, as demonstrated in But I Have A Receipt and Free Cake, not yelling at Muscle Man when he put "My Mom" on the list. He does not confront Muscle Man when he unzips his pants in "Free Cake", saying, " It's not that kind of party Muscle Man."

Other Employees
There is minimal to no interaction between Muscle Man, Skips, and Pops. They had to take care of Rigby in "Death Punchies", but besides that, there is not much. It is seen though in "Rage Against The TV," that they will work together to fight a common enemy.

Trivia

 * He appears to be something resembling a zombie or Frankenstein's monster, which would be further evident with the fact that he is commonly seen with his undead friend, High Five Ghost.
 * It is confirmed in Muscle Woman by Mordecai that Muscle Man is a human being.
 * In "Don", Muscle Man is fired by Benson because he made a snarky comment about his own mother, saying that getting fired "was worth it." However, he shows up for work in the next episode.
 * Him and High Five Ghost both got an appreciation plaque in "Appreciation Day."
 * While Muscle Man is very muscular, it is only noticable when his arms are visible because it is hidden by his fat.
 * Mordecai and Rigby are shown to have fun by throwing stuff (mainly bologna) at Muscle Man's car.
 * He can play a mean "piece of brass", as seen in This Is My Jam.
 * Muscle also appears to be drawn similarly to characters from " The Marvelous Misadventures Of Flapjack", a Cartoon Network cartoon J.G. Quintel helped on before starting Regular Show.
 * More often than not, Muscle Man removes his shirt during the episode he appears in.