He appears a foreboding human in a red cloak and a mask covering his mouth. His only fear is his cloak getting chewed on. His main goal is to find the Power Pellet Forest and use its power to take over Pac-Land.
Mezmeron seems to never want to do anything himself; his main role in the series is to give orders to the Ghost Monsters Inky, Blinky, Pinky, Clyde, and Sue. He verbally & physically abuse them if they do something wrong, which happens a lot. Even though he's able bodied and quite powerful and resourceful, he only ever attacks the Pac-people himself when the Ghost Monsters are acting even more useless than normal.
It has been shown that Ghost Monsters are able to wear his cloak after being chomped by Pac-Man. Mezmeron has an entire closet full of identical cloaks in the same room where the Ghost Monsters extra skins are kept.
Mezmeron and his schemes typically only appeared in one of the two Pac-Man cartoons each episode, the other featuring the ghosts merely annoying the Pacs on their own. This pattern was kept to in the special, 'Christmas Comes To Pacland'.