Events prior to the manga
Not much is mentioned, though at some point he is befriended by Hana.
Role in the manga
Stank, who might represent a wild side (the Jim Henson Company also worked on Where the Wild Things Are, and there are even some references to that story here and there) or the kind of simplistic strength Ludo represented, is there mostly as a ride for Hana, a fairy who lost her wings as punishment by goblins. While Ludo is a "noble beast", Stank has a role filled with toilet humor, from smelling like bowel movements to urinating on other characters. Like Ludo, his rock-summoning powers become very helpful in battles.
Stank looks like a smaller version of Ludo, having a round body, thick fur, and two short, twisting horns.
Like Ludo, he can make rocks and bricks move by calling out to them. Like Ludo, he speaks only in short one- or two-word phrases. Although good-natured, Stank has a number of unhygienic habits.