Zombies inhabit the world in which Maxx lives in and their main goal is to eat people. They are slow and they are many in numbers. They first appeared in comic #14.
Usually, zombies communicate with different variations of the word "grah". In comic #44, however, it's shown that zombies can speak the same language as humans.
Zombie, comic #44
Zombies are the cause of Cyril's first death and are one of his many phobias.
Turns out some Zombies are open to all types of relationships, as in the Zombies that kill Cyril think that he and Maxx are a couple having marital problems(comic #15).
In comic #433, it's shown that Xylan can summon zombies.
They also killTyrone in his first appearance.