Scarlet Personage

The Scarlet Personage is a villain from Conan the Barbarian but is also a part of the Marvel universe itself, since the story took place in a time when Marvel had rights to the Conan character and ideas for comic use, as a result the figure has become an enigmatic entity that may be one of many alter-egoes created by Death itself.

Appearance
the Scarlet Personage can take the form of a humanoid male with a bandaged face or a "blind" ferryman known as Bracca (who dressed in a robe which concealed most of his features) : the entity could also reveal a rotting red skull and even appeared as a disembodied face, showing it could take non-humanoid forms at will.

Abilities
The Scarlet Personage had a vast array of supernatural powers, with no real limit, the creature could draw strength from horror and fright, especially a fear of death, allowing it to attack with great strength at opponents, it could alter reality (or at the very least the minds of those around it) so as to inflict horrific illusions and enter dreams : it could change forms and quite possibly had nigh-omnipotence, since it was implied to be a personification of Death.. while Conan apparently defeated it by throwing its physical body overboard this only seemed to cause it to create powerful storms, suggesting that it is a truly immortal being capable of manipulating events even after a "physical" defeat.

Trivia

 * the Scarlet Personage disguising itself as a ferryman is a reference to Charon, the ferryman of the Greek Underworld - who is also deeply associated with personifications of Death in fiction.
 * Conan spitting at the monster's face to defeat it is symbolic of Conan defying the fear of Death itself, which is what the Scarlet Personage likely embodied and thus allowed him to "defeat" the entity.