Despite being one of the two main protagonists of the series, he also has done antagonistic acts which also makes him a protagonist villain, however he has done things to fix his mistakes along with Rigby (who is usually the one who causes it in the first place).
He is voiced by J.G. Quintel, the creator of Regular Show along with High-Five Ghost.
Mordecai would be best described as mild-mannered and laid back and big hearted. Like Rigby, he lacks clothing, plays video games, and he drinks copious amounts of coffee and soda. Out of the duo, Mordecai displays far more patience, intelligence and responsibility than Rigby does. Even though almost every problem in every episode that was caused by the duo is Rigby's fault, Mordecai puts up with his laziness and immaturity, once filling out a job application for Rigby because he claimed it was "boring". Mordecai tends to be more sociable and friendly than Rigby, and has much more manageable relationships with others.
However, Mordecai can sometimes be a jerk to Rigby such as making fun of him for his shortcomings, repeatedly punching him when he was jinxed, replacing him with Skips as his teammate for the video game tournament, and making fun of his new name "Trash Boat", but despite bullying Rigby at times, he is a true friend.
- He is sometimes a bully to Rigby and punches (it's usually for Rigby being a jerk or an idiot or both) or humiliates him for his amusement.
- The Power: After Rigby steals a keyboard from a wizard, he and Rigby start wishing for things which Skips was against.
- Death Punchies: He made fun of Rigby's buttcheeks along with Muscle Man.
- Grilled Cheese Deluxe: He and Rigby challenge each other on who is the expert liar and lie that they're astronauts and spend the whole episode lying until they revealed that they weren't astronauts.
- It's Time: He microwaves all the clocks in the house to prevent Rigby from finding out what time it is for his date with Margaret and kills him by pushing him off the microwave in anger when they get sucked in another dimension crossing the Moral Event Horizon.
- Appreciation Day: He and Rigby write lies in the Book of Park Records to make themselves seem like better employees than they already are. This leads to the creation of Snowballs the Ice Monster and the near destruction of The Park.
- Jinx: He repeatedly kept punching Rigby when he was jinxed.
- Karaoke Video: He and Rigby excitedly manage to accidentally trash talk Benson, Pops, and Skips.
- Bet to Be Blonde: He kidnaps Rigby and tries to douse him in an extremely hot blonde pit but he was actually trying to get him to tell the truth that he cheated on the bet.
- Video Game Wizards: He makes Skips instead of Rigby play with him in a video game tournament despite Rigby being his best friend but redeems himself in the end by making Rigby his teammate.
- Trash Boat: He along with Benson, Pops, Skips, Muscle Man and High Five Ghost make fun of Rigby's new name "Trash Boat".
- Laundry Woes: He doesn't listen to Rigby trying to tell him to get over Margaret when they try to give Margaret her sweater and kicks Rigby out of the car when he calls him a "sad sack chump".