Originally named Galan, he is the sole survivor of the Big Crunch of the previous universe. A space explorer investigating the impending end of his universe, he approached the focal point of the Big Crunch and was transformed into a cosmic entity even as the universe collapsed. After the Big Bang of the current universe, to complete his transformation, Galactus was encased in a cosmic egg brimming with enormous energies. After billions of years, he emerged as an entity of vast cosmic power who was also necessary for the existence of the newly formed universe. Galactus is considered one of the three essential entities within the Marvel Universe alongside Eternity, the anthropomorphic personification of the universe, and Death.
Though he wields the Power Cosmic, Galactus must feed off the energy of planets, without which he cannot survive. Towards this end, Galactus scours the universe seeking planets to sustain himself. Over millions of years he has become one of the most feared beings in the universe, his vast power allowing him to laying waste to innumerable extraterrestrial civilizations in his quest for sustenance. Nevertheless, he is not evil, but rather a force of nature.
He has appointed a number of entities as his heralds, imbuing them with a portion of the Power Cosmic and setting them out to search for edible worlds. Most of his heralds have rebelled or betrayed him. Among his heralds are the Silver Surfer (formerly Norrin Radd of Zenn-La), Terrax the Tamer (formerly Tyros of Biroj), Firelord, Gabriel the Air-Walker, Nova (formerly Frankie Raye of Earth), Morg, and Red Shift.
Recently, in the Galactus: The Devourer limited series (1999-2000), Galactus was changed into a star by the forces of the Earth heroes and the Shi'ar Empire. The results of this fact were told in the X series written by Alex Ross.