In-Betweener is a fictional character, a comic book cosmic being in the Marvel Comics universe.
The In-Betweener is a cosmic being, an incarnation of balance and duality. In him exist the dualities of life and death, reality and illusion, good and evil, logic and emotion, existence and nothingness, god and man. He is an agent of Lord Chaos and Master Order.
Adam Warlock and Doctor Strange have had encounters with this being, and Thanos stole one of the Infinity Gems from him.
In the dimension ruled by Lord Chaos and Master Order, he is the power equivelent of Galactus. He is beyond the touch of standard science and magic. When he met Galactus in combat, he realized that, as the union of all opposites in the universe, it made Galactus his exact opposite, because Galactus existed in his universe with no opposite against him.