Gaea was one of the Elder Gods who materialized on Earth before any life appeared there. She and her brother Chthon inhabited Earth's land masses, affecting geological patterns. Except for Gaea, the Elder Gods degenerated into demons, preying upon each other. Gaea called upon the Demiurge, the sentient life force of Earth's biosphere, and gave birth to Atum, who became Demogorge and slaughtered the other Elder Gods, though some, like Chthon and Set, escaped extradimensionally (Note: Many beings incorrectly refer to themselves as Elder Gods). Gaea infused her life essence into all living beings on Earth. She protected Earth from the influence of Set, supporting the development of humanity over dinosaurs and leading the Celestials to destroy a group of Serpent Men.
Gaea became the mother god to virtually all of the pantheons of later gods in humanity, receiving many different names. In her guise of Jord she mated with the Asgardian god Odin to conceive Thor. A millennium ago she learned of humanity's future judgment by the Celestials and organized goddesses of numerous pantheons to gather the best examples of humanity. This resulted in the Young Gods, whose existence swayed the Celestials to judge in humanity's favor in the 21st century.
Gaea continues to grant power to many who call on her, from the ancient Sisters of Danu to the modern Ardina, Brother Nature, Clea, Dark Mairi, Doctor Strange, the Neurii, the god Prometheus, and Topaz. She has even directed opposition to threats such as Dormammu (who once held her prisoner until she channeled the life force of every being on Earth to banish him) and Maelstrom. Her pain resulting from the harm humanity had done to Earth, nearly drove the mutant Humus Sapien to take the lives of all mankind. She was captured by the extradimensional scientist Yandroth and forced to place a curse on the earliest Defenders, compelling them to gather to oppose threats to Earth. She continued to perpetuate this curse herself for a time, pleased to have even unwilling protectors, but she dissolved it after the Defenders became corrupt due to Yandroth's influence. She informed Nighthawk that he would have the power to summon them should the need arise.