Death can manifest itself on the physical plane at certain times to certain individuals as a sentient, quasi-tangible humanoid entity of either gender. Like Eternity, Lord Chaos, and Master Order, Death is an abstract being embodying a concept, whose true nature and origin is unknown. Death and the being called Eternity are said to comprise the mystical essence of the universe: Eternity embodies the principle of life, and Death embodies the principle of mortality.

Death and Eternity can both manifest themselves as sentient beings, and have spoken of themselves as siblings. They have appeared in humanoid form, although presumably they could appear in any guise they chose. Eternity generally appears in the form of a male, while Death usually manifests itself in female form. This may simply be the form Death chooses to seduce males into doing its will. When Death presented itself once to the vampire lord Dracula as a rival rather than as a seducer, it took male form. While Death can take the guise of a living human, it more often appears to living beings as a hooded, robed skeleton.

The personification of Death sometimes seems to possess fathomable motives. Death seems to seek new conquests, and manipulates mortals with or without their knowledge in order to gain them. Death once attempted to destroy Dracula through human pawns because Dracula was depriving it of conquests by creating vampires who were neither truly alive nor truly dead Death failed on that occasion, but Dracula eventually fell victim to permanent destruction. Although Death ordinarily seems content to maintain a balance in the universe between its power and Eternity's, Death will seize opportunities that arise to achieve dominance over Eternity. Death once appeared to the mad Titanian Thanos in the form of a woman with whom he fell so much in love that he was willing to destroy the universe in order to please her. Death also apparently works in partnership with Galactus, the destroyer of worlds. Death has on occasion taken the role of gamesman, having once played a tournament of champions with the Elder called the Grandmaster.

Death's ultimate goals are unknown. There may be a master plan guiding its movements or nothing more than random chance. Virtually all living creatures in the known universe must eventually surrender themselves to Death. Even the Eternals and Asgardians age, although they do so very slowly, and will someday die. The Olympian gods do not age, but can be killed by a sufficiently powerful force. The Elders of the Universe, reputed to be the oldest living beings in the universe, can also be killed by a sufficiently powerful force. Galactus, the only known entity said to predate the Big Bang itself, believes his death inevitable.

The relationship between Death and the so-called gods of the dead of the various pantheons is also very hazy. Death gods like Hela and demons like Mephisto seem to receive certain undefined powers from Death and even rule over extradimensional realms seemingly inhabited by the souls of deceased mortals. But whether they are Death's pawns or allies cannot be determined.

Death remains one of the greatest mysteries of the universe. At one point, Death was "killed" by the extradimensional being known as the Beyonder, who later "recreated" it. The implications of this on Death's nature are still a mystery. Later, Death appeared to the Phoenix Force, claiming it to be the product of power of all life yet unborn, and thus somewhat an agent of Death and abstract entity the likes of Eternity and Death. Death helped to convince the Force to leave its then-current avatar, Rachel Summers.

More recently, Death has seemed to take a fascination with the villain known as Deadpool, appearing to him on several occasions in the context of a somewhat romantic nature. Again, the implications of this are still a mystery, even to Deadpool.

First Appearance: CAPTAIN MARVEL #27