Monsters in space!

Zack is shocked when he goes to school one day and finds a monster in his seat! Who/what is this creature? At first Zack is scared, but he soon finds that this monster, Al, is kind and friendly. Zack and Al become fast friends, and Zack goes to Al’s planet and meets all kinds of other monsters. Zack realizes that just because Al looks different, it doesn’t mean that he’s weird or strange.