Galactus was created during the union of the Sentience of the [previous] Universe and Galan of Taa, and a herald described him as "the physical, metamorphosed embodiment of a cosmos." Galactus considers himself a higher being than all non-abstracts, maintaining his existence by devouring planets with the potential to support life.
Although not an abstract, non-corporeal being, Galactus is a living force of nature set on correcting the imbalances between the conceptual entities Eternity and Death. His true form cannot be perceived by most beings; each species sees Galactus in a form they can comprehend, similar to their race or a deity of their religion. Galactus has also appeared as a humanoid star when addressing fellow members of the cosmic hierarchy.
As Galactus feeds to sustain himself, he must wear armor to help regulate his internal energy. Due to this hunger, Earth's heroes have been successful in defeating a weakened Galactus.
The only thing able to instill fear in Galactus is the Ultimate Nullifier. He also has the heralds, servants of Galactus who wield the Power Cosmic he gave them. The only one seen so far is The Silver Surfer.
He has a daughter named Galacta. She appears in many titles as a playable character with weakened powers that Galactus uses in his own boss fights.
Mysterious Five Project
In the events of the Mysterious Five Project, Silver Surfer accidentally lead Galactus to Earth. Inori and Chuck remembers about going into Anti-Space and the fact they could see the entire universe from there. Dexter and Iron Man build a portal to Anti-Space as Galactus heads towards the Earth. Doom Mecha shoots off some Irregular Energy to delay his arrival, holding him so Inori and Chuck can figure out some sort of solution to stop Galactus. They stick their heads out so they can see what’s going on, and they see Galactus being controlled by a hand. Just then, a nuke comes from Degen, intending to blast Dr. Doom. Wanting to destroy everyone, Degen sends the nuke to destroy the Doom Mecha. Silver Surfer grabs it though, and heads into Anti-Space and releases it, hitting the hand that is controlling Galactus. Galactus falls to Earth severly weakened and the heroes fight him off.
Just as they defeat him though, Agent Venom’s symbiote is attracted to the static Irregular found Galactus and detaches from the Agent and goes on Galactus. Symbiote Galactus destroys the Doom Mecha, thus creating a battlefield. Symbiote Galactus grabs Spursverse Mario and Lapisverse Mario and creates portals to the Lapisverse and Spursverse, intending to take them over while taking over this universe. The universal cracks begin to break even more before finally cracking entirely, creating a huge dimensional rift of every baby waffle universe ever created. Symbiote Galactus heads towards the prime universe, the Fisticuffs Universe.
Glass Canyon is the only area left from the original Mysteriousverse, so they head back there to free everyone stuck in the Glass Canyon and tells them what is going on. Symbiote Galactus breaks the veil of the Fisticuffs Universe but is knocked back by the Titans, with Inori and Chuck E. Head appearing with Dexter, Iron Man, Dr. Doom, Emmet (who is in a mecha), Spursverse Mario and Lapisverse Mario.
Silver Surfer comes into view and pulls out the ultimate Nullifier. Symbiote Galactus merely shrugs as he uses it, being infused with so much Irregular from cracking the Mysteriousverse. Iron Man and Dexter pull out two more (found in the Spursverse and Lapisverse) and on the count of three they use it. The sheer power finally manages to knock both the symbiote and galactus out. The Irregular Energy disperses, repairing the broken universes, but creating presences of everyone who walked in there, creating multiple clones of the same characters through out the other universes. A portal to Anti-Space opens and they toss Galactus out through there, making sure he will no longer harm any more of the universes.