Agamotto was an extremely ancient and powerful magic entity of order. He and the fellow-minded Oshtur and Hoggoth formed the omnipotent trio known as the Vishanti.
Why don't you run along home and chew on your furniture, before I painfully remind you that you were once just a plain little man named Galan! The Eye, of course, stays here... and so does Doc. I get so lonely...
Agamotto was born from Oshtur, benevolent Elder Goddess of Earth. His journey to discover the secrets of magic and find Oshtur led to the formation of the paths of magic power. Agamotto also served as Earth's first Sorcerer Supreme, defending it and its reality against such threats as Dormammu.
Doctor Druid was forced to unmake Agamotto's Moebius Stone, but not before it transformed Cody Fleisch into Cadaver, Agamotto's avatar.
During the War of the Seven Spheres, the Vishanti battled their rivals, the Trinity of Ashes. Despite an initial refusal, Doctor Strange was enlisted to serve them in the war. After their victory, he was returned to Earth.
Agamotto's appearance varied when he was encountered in his realm. He was known to appear to Doctor Strange as a caterpillar smoking a pipe in a realm that appeared to be out of Alice in Wonderland, capable of human speech and unintimidated by Galactus. He is actually the entire dimension itself, as was why Galactus was unable to destroy him permanently. During a quarrel with Galactus, he assumed a more menacing version of the same form. When the Vishanti appeared as a group, Agamotto took on the form of a caterpillar.
When Silver Dagger was placed into the dimension, Agamotto tried to convince him to stay. Silver Dagger eventually escaped. This was later revealed to be a ploy by Agamotto to see if Silver could change when in possession of an old version of the Eye Of Agamotto.
Agamotto and the Vishanti were worshiped at the Temple of the Three. His avatar was Cadaver.
Agamotto was behind the demonic invasion of earth as he saw the previous Sorcerer Supreme as a failure and the current one as inexperienced. But the current Sorcerer Supreme sacrificed his life to kill of Agamotto from taking over the world by blowing up the eye and orb of Agamotto with him.
Despite his death however, Agamotto still has a mystical connection to Iron Fist whom he previously trapped in his dimension[1] when his power had possessed Iron Fist in interfering with the Immortal Weapons mission in closing the gate to the Eighth City until War Machine knocked Iron Fist out.
As the Sorcerer Supreme of the Marvel Universe, and the spawn of an Elder God of Earth, a realm where magic appears especially attuned, Agamotto possesses extremely powerful magical abilities, which he can channel to certain mystics, mainly the Sorcerer Supreme of the mainstream Earth dimension, sufficient in strength for him to usually defend his reality. Agamotto has held his own against entities of such power as Dormammu and Galactus on several separate occasions when they clashed, making it apparent his full power can rival either's. It has been hinted that he is more powerful than both Oshtur and Hoggoth combined, despite being the spawn of the former. As the Vishanti, their power and omniscience is even further magnified. Agamotto specializes in divination and truth, such as the Eye of Agamotto's all-revealing light. Agamotto is described as "all-knowing," implying omniscience in dimensions even beyond his own, or at least potent mystic sensory abilities; so powerful are his abilities to gather knowledge that he is even prone to knowledge concerning cosmic entities in other universes, such as Galactus, aware that he had been Galan and of his origins. Such is the magical potency of Agamotto that the Sorcerer Supreme, Doctor Strange, was unable to banish him back to his own realm, even when invoking the united strength of Dormammu, Cytorrak, Watoomb, Raggadorr, Denak, the Seraphim, the Faltine, Ikonn and Valtorr to fuel the spell. Agamotto is even capable of resurrecting others, as he did to Cadaver, as well as opening time portals.
Agamotto's "pipe" is actually a powerful magical artifact that assists Agamotto with his magics. He is also in some way powerfully linked to the Orb of Agamotto and the Eye of Agamotto, able to recall them across dimensions from even the grasp of a Sorcerer Supreme at whim.