Hellblazer

Hellblazer is a comic published by DC Comics. The series stars John Constantine, a surly home-grown wizard only slightly more pleasant than the monsters he deals with. Over the years he's travelled across Britian and the US dealing with all sorts of monsters, both supernatural and unfortunately natural.Hellblazer was one of the few titles unaffected by DC's New 52, remaining a Vertigo imprint.

They also made a movie, although stangely they renamed the character to John Constantine Asshole. Possibly this was an attempt to appeal to a younger demographic.

Demon
Gemma Masters, John's niece, is something of a wizard herself. She also has a bone to pick with John due to blaming him for raping her at his wedding reception (which was actually a demonic doppleganger of John). To deal with her problem she summons a winged demon in Ish #179 to kill John. After leaving John to be torn apart at the hands of the demon she has something of a crisis of faith and goes to John's wife Epiphany. She eventually chooses to believe her that John was uninvolved in the rape, and returns in time to, with help a potion of Epiphany's, kill the demon.