Leonard is a 17 year old human who has thin legs and arms compared to that of Finn's.
Leonard has dark ginger - brown like swooping hair. The bottom half is tied into a ponytail.
As seen in his picture, Leonard wears a top hat with goggles, a shirt with a brown vest and a red tie. On both hands, he wears buckled gloves and has a rusty mechanical arm on his left during the results of his arm cut off. He wears a pair of highwaist pants with white boots. It was revealed that on his left mechanical arm it said "Smarten Armen, Made in Germany".
Leonard wields a samurai sword named Yamoto, a blade which can cut through anything, even platnium.