Erlik

Erlik was a Hyborian Era deity from Marvel comics, though he is part of the mythology of Conan the Barbarian - a franchise that doesn't fully belong to Marvel (although the company did have rights to the character for a while).

Erlik was active long before the current Marvel time-line, during the era that Conan the Barbarian existed (which was in the distant past, nearing the beginning of human civilisation) - this makes him a very ancient deity, possibly connected to the Elder Gods themselves: however he didn't seem very active in the modern era and as such was mainly an opponent to heroes that existed during Conan's life-time.

Erlik was a harsh deity who believed in hardening humanity's souls and loyalty via trials and deprivation - this earned him the title of "god of evil" amongst those that opposed his ruling style and indeed he often had a demonic presence (though it was never revealed whether this was his true form of merely guises he took in order to intimidate mortals).

As well as the ambiguous title of "god of evil" Erlik was a death deity and as such could resurrect the dead as well as grant immortality, regenerative abilities or a "death touch" upon those he favored.