Leo is the ruler of Sector: LXVI (66) in Hell. He rules over lower class subjects while also having to watch his subordinates. Along with other demons that don't fall under the category in the Incubus race, he also has to make sure each incubus goes out and forms a contract with a usable soul at SOME point.
On a different note, he acts very immature and has a smart mouth. He hates his job and would rather be wrestling with his other friend who is also a lord and dragon, or playing with his hell hounds.