Galactus is a Marvel Comics character and supervillain from the animated television shows The Avengers: Earth's Mightiest Heroes, Ultimate Spider-Man, Hulk and the Agents of S.M.A.S.H., and Avengers Assemble. Galactus is an extraterrestrial being who lives on an artifical planet called Taa II. He is known as the planet destroyer because he eats the planets whole. His powers are the Cosmic Energy that is in him. He can take some of his own Cosmic Energy and give it to a living creature and turn him into a herald. He is the enemy to the Fantastic Four and the Silver Surfer.
In the episode "Prisoner of War", it is revealed that he was responsible for destroying the Skrulls' homeworld. Galactus finally reaches Earth and sends his four heralds, Terrax, Firelord, Stardust, and Air-Walker to different parts of the world to install its energy conduit towers and prepare the planet for consumption.
The Avengers, alongside the other heroes of Earth, are divided into groups to destroy each tower and his Herald. One team, composed of Mr. Fantastic, Doc Samson, Iron Man, Ms. Marvel, and Yellowjacket (Henry Pym) is dispatched to Galactus' space vessel.
When each Energy Conversion Tower is destroyed, Galactus teleports himself to the surface and re-assembles his towers using his remaining Cosmic power and begins to feed to himself.
While the Avengers battle Galactus, Mr. Fantastic and Iron Man make a portal to the Negative Zone and key it to the energy signature of Galactus' Cosmic energy. Galactus resists going, trying to pull himself back into the main universe, but final blasts from Iron Man and Thor send him through the portal, which seals behind him. Galactus, now trapped in the Negative Zone, feeds on the anti-matter and no longer eats planets.
Galactus was summoned to Earth by his hearld Terax the Tamer. But instead of eating the Earth he came to earch for a new herald (She-Hulk) to replace Terrax. Once the new herald did not want to join him, Galactus attack the planet by activiating his ship Taa II and battled against all the Hulk's. In the end Hulk through the fight and Terax was returned his powers.
In the two-part episode "Planet Hulk," Ronan the Accuser and the Kree use Ego the Living Planet to be a sacrifice to Galactus. During this time, Galactus is shown to have Firelord as his new herald where Firelord claimed that Terrax failed him. Hulk had to work with Ego's inner-ego to keep Galactus from consuming Ego the Living Planet. After Hulk and Ego the Living Planet defeat Galactus, Firelord leads Galactus away to find an uninhabited planet for Galactus to consume.
When Galactus arrives to consume Earth, Iron Man ends up having to speak with him which results in both of them teleporting away. The Avengers track Iron Man to the planet where the D'Bari live and witness their ships in the middle an evacuation after Iron Man (who was empowered by the Power Cosmic) led Galactus here. The Avengers had to work with the Guardians of the Galaxy to keep Galactus from consuming the planet. It later turns out that the planet that Galactus was consuming was becoming unstable before Galactus arrived. Galactus found himself unable to stop the process as the Power Cosmic-empowered Iron Man quotes "Galactus must feed." After the planet exploded, Galactus was knocked out cold, the D'Bari settled on another planet, and Iron Man returned to normal.