Melman is an elderly Cappy and the one mailman of Cappy Town. Based on his knowledge of where people live, one can infer that he has a good memory. In the episode Born to Be Mild - Part II, it is discovered that he is also the legendary biker, Steppenwolf.
Steppenwolf is Melman's alter ego. He is a legend among bikers according to Gus when he revealed that he had been part of Fang's motorcycle gang when he was younger. Steppenwolf asserts that being a biker isn't about breaking laws and being a vandal—it's about freedom. He hadn't been seen in years at the time.
Steppenwolf is simply Melman garbed in a Gothic gray T-shirt with a heart on it and wearing a light brown vest over it, as well as a belt. He wears a green bandana and a brown helmet over it, and wears sunglasses. He rides on a red motorcycle.
Later, Fang, Rip, and Turbo roared into Cappy Town looking for Steppenwolf, who eventually went back in business during the village's second race. He entered the race to help the others best Fang in the race. After easily besting Fang again, Steppenwolf left the Dedede speedway, where the second race was held. Later, as the speedway crumbled, burying Wheelie in the rubble, Kirby and his friends found out in surprise that Steppenwolf was Melman (which could have been seen due to the remarkably similar look on the two of them).
His name is based on the word "mailman," referencing his occupation.
In one of the episodes of the anime, Melman swears he doesn't read any of the letters he is supposed to deliver. This is contradicted in another episode, as he mentions that he looks over King Dedede's mail before mailing it to him.