Islam has a whole host of
Angels, (kinda like the Christian's but funkier ;) ), and
Archangels, of which
Izra'il is the Angel of Death.
He is part of a group of Archangels responsible for the cycle of life and death. In this cycle Jibra'il (or Gabriel) is the life creating Angel (he also delivers important messages from Allah when the occasion requires it.)
Mika'il (or Michael)is the life sustaining Angel, who keeps us alive during our term. Finally there is Izra'il who ends life and takes us into the afterlife for our eternal reward. There is also one other Archangel, and he is Izrafil, whose Job it is to Herald in the Last Day and begin Armageddon.
There is no darkness associated with Izra'il in Islam, he's got a job to do like the rest of us, and without him we'd probably be hanging around wondering what to do after we had ceased to live but before we had properly died.
His alias in Christianity is Azrael, as those of you who've studied the the faith carefully will undoubtedly know. I'm not sure whether there is an equivalent in Judaism.