This is one of the two demons a demonologist may summon. A female demonologist will have an incubus, while the male demonologist gains a Succubus instead. They are equivelant, aside from the skins.
At the moment, all 5 demons appear to summon an incubus or succubus. This may change later; a Demon Servant and a Demon Warlord are hardly expected to look the same.