They are often amongst the most powerful and important entities in a given tradition, reflecting the fact that death, like birth, is central to the human experience.
In such dualistic models, the primary deity usually represents good, and the death god embodies evil.
Similarly, death worship is used as a derogatory term to accuse certain groups of morally abhorrent practices which set no value on human life.
In monotheistic religions, death is commonly personified by an angel or demon standing in opposition to the god.
A single religion/mythology may have death gods of more than one gender existing at the same time and they may be envisioned as a married couple ruling over the afterlife together, as with the Aztecs, Greeks, and Romans.