They are responsible for being the creator of the Eternals, the Deviants, and the Celestials as both writer and artist. The Eternals is the spiritual successor to The New Gods published by DC Comics and also created by Jack Kirby as both writer and artist. The Eternals was inspired by the book Chariot of the Gods and was originally designed to be separate from the Marvel universe for creative freedom.

They are responsible for the creation of the Titans. Kronos, Uranos, Oceanus, A'lars, and Sui-San are Titans who were retconned to be true Eternals from Earth whilst Thanos and Eros were retconned to be true Eternals from Titan. They also contributed to the creation of Titanos which was retconned to be the first home of the Eternals and they are also responsible for introducing artificial Eternals of Titan.

They are responsible for integrating the Eternals into the Earth-616 Marvel universe. They are also responsible for attempting to complete the narrative that Jack Kirby tried to complete with his Eternals series through their Thor series. Their integration of the Eternals into the main Marvel universe meant these beings were confused by humans as being the same entities from various mythical pantheons.

They are responsible for combining the mythology of the Eternals by Jack Kirby and Roy Thomas with the mythology of the Titans by Jim Starlin. They revealed which Celestial created the Deviants and which Celestial created the Eternals and expanded the Titanos mythology via What If? #23-#28. They also introduced various Eternals exclusively through The Official Handbook of the Marvel Universe.

They are responsible for establishing the foundation of 100 true Eternals and the existence of The Machine which was introduced as The Archives, Earth's inter-planetary system responsible for the resurrection process of the Eternals. They also expanded upon the mythology of the renegade Celestial by Jack Kirby who was officially unveiled as Tiamut the Dreaming Celestial, the creator of Makkari.

They are responsible for establishing the different Eternals factions within Eternal society, introducing the three principles of the Eternals, having all 100 Eternals be birthed at the same time, introducing excess deviation for the Deviants, and creating 40 new Eternals to co-exist with the pre-existing 60 Eternals. They also rebranded the Eternals as the cosmic angels of the Marvel universe instead of gods.