An Appellomancer is a name wizard with the ability to grant new names to others.
Thereafter, the renamed individuals seem to live out their new names and the people around them expect them to embody their new names (Princess Fatherfucker, for instance, begins a sexual relationship with her father while Captain Cockstink's genitals are perceived to have an unpleasant odor by those around him). However It is never stated if the individuals are magically forced to live out their new names or if they choose to.
Only a single Appellomancer is ever shown in the comic Branding.
Though it is not stated if all Appellomancers are evil, Princess Fatherfucker states that the one who granted her name was evil and the one shown in the comic Branding is at least depicted as vengeful when Appellomancers in general are mocked as she immediately grants the mocker the name "Captain Cockstink."