[2] The In-Betweener is a cosmic entity who represents duality and serves fellow conceptual beings Master Order and Lord Chaos, although his loyalty is usually to himself rather than to them.

Thanos then steals the gem and abandons the In-Betweener to face the wrath of Master Order and Lord Chaos, who discover he has escaped his prison.

[13] After the universe is restored, Order and Chaos kill the Living Tribunal and force the In-Betweener to fuse them into a new cosmic being named Logos who can replace him.

The In-Betweener's other major (and unique) ability is to analyze a target and then direct energy towards it in a "polar opposite" form, which is instantly fatal.

[5] Alternatively, if he cannot personally synthesize the "opposite energy" necessary to eliminate an opponent, he can directly summon that enemy's opposite being, and eliminate them that way; using the power granted to him in his station as a cosmic force, he once even summoned and forced Death itself to destroy the Elders of the Universe, even though it had, at an earlier point, refused to ever let them die again as a punishment.