Like Eternity, Lord Chaos and Master Order, and Infinity, Death is an abstract entity embodying the concept of the mortality and extinction, inasmuch as its opposite, Eternity, embodies life. Death and Eternity even regard themselves as siblings, having come into existence at the moment the universe was formed.
During the times that Death has manifested itself on the physical plane, it often takes the form of a skeletal female; however, the body Death chooses to manifest as can be in any form or size.
Death's motives and modus operandi are hard to fathom. It works in some kind of partnership with Galactus, a being who survived the destruction of the previous universe, and also provides some measure of power for Death-gods like Hela and demons like Mephisto, who are allowed to rule in her name over extradimensional realms inhabited by the souls of the dead.
Death seems to be always seeking out new conquests and may manipulate mortals with or without their knowledge in order to gain them. Death once attempted to destroy the vampire lord 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 occasions, 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 Titan 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. Indeed, nearly all of Thanos' activities from that point on involved his desire to win Death's favor. When Thanos possessed virtual omnipotence by means of the Infinity Gauntlet, however, Death, for reasons of its own, turned its back on him. Thanos himself has yet to fathom Death's motives for this relationship.
Death has on occasion taken the role of gamesman, having once played a tournament of champions with the Elder to the Universe called the Grandmaster, the end result of which proved the Grandmaster and fellow Elders immune to Death's power.
At one point, Death was "killed" by 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.
Death has seemed to take a fascination with the mercenary 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.
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 offshoot of humanity known as the Eternals and the otherwordly Asgardians age, although they do so very slowly, and will someday die. Olympians do not age, but can be killed by a sufficient powerful force. Galactus, the only known entity said to predate the creation of the universe itself, has since died. Death remains one of the greatest mysteries of the universe.