The fictional Marvel Universe contains a number of beings in this category that are literally part of the universe, with their existence necessary to provide a certain function. Much like organs provide specific functions for the human body, these entities provide functions for the universe itself. There is no official (known) name for these beings, but they are often referred to as cosmic entities, cosmic beings or abstract entities. Many of them embody some concept or fulfill some essential need, but there are others who are considered within this reference frame simply due to their scale of power, such as the Infinites, Beyonders, Cosmic Cubes, or Watchers. Death is also considered to be a cosmic entity.
Each cosmic being is unique, but they often have the following characteristics in common:
Power greater than that of virtually any mortal being, with extremely rare exceptions. Note, however, that their level of power greatly varies, with some being able to affect the entire space-time multiversal reality. The Living Tribunal, Eternity, Master Order, and Lord Chaos were once referred to as meeting in 16-dimensional space.
No physical form. To visit the material universe they may use 'M-bodies', life-forms created for them by an entity called Anthropomorpho in the 'dimension of manifestations.' The power bestowed upon a manifestation body is said to be directly dependent on how well any given creation is able to 'synchronize' with their assigned entity. Such bodies can also be employed by uniquely prominent physical entities, such as the Stranger or Galactus.
A completely amoral nature, uncaring about anything but their purpose of existence, and frequently to safeguard their Universe (i.e. themselves) from destruction, although some have recurrently displayed personal, or even human-like sentiments, and sometimes are not above remorse. A notable example of this is Galactus; despite his consumption of living planets, he occasionally displays disgust of his mission. In fact, he states that he feels an intense kind of guilt for all the civilizations that he has destroyed, and cannot close his eyes without recalling the ghosts of the beings that have died as a result of his feeding.
In the fourth Eternals limited series, by writers Charles and Daniel Knauf, the Dreaming Celestial states that "Every component in the physical Universe is a model/example/function of balance... Every particle/being/concept/action exists in this state of sublime equilibrium to serve [a being known as] the Fulcrum. And when asked by the Eternal Makkari whether "every cosmic being in this Universe is a total tool", replies "Yes. We are all tools of the Fulcrum".
The Marvel Universe versions of the gods of most earthly religions, excepting Christianity, Islam and Judaism, are not cosmic in the traditional sense, although the strongest of them, such as Atum and Odin, can rival or exceed the power of certain cosmic beings, as can the most powerful demons or independent mystic entities such as Zom, Dormammu, Shuma-Gorath, Mephisto, Cthon, or the Vishanti, and, per extension, the sorcerer supreme, Doctor Strange, at times when he channels their full power, but their existence is not necessary for the universe to function. Others pretend to embody existential concepts, but lack the power of the true entities, such as the demon D'Spayre who has claimed to embody despair, but in rare cases, such as Nightmare or Amatsu-Mikaboshi it depends from story to story whether or not they are considered embodiments. Exactly how many true cosmic entities exist is unknown, and more keep being revealed as time passes.