Adversary is a character who appears in the comic Turtle Soup vol. 1.
Adversary is an evil spirit that is a conglomeration of all the rats in prehistoric times that ate the eggs of the mythical Great Turtle. Feeding off the Great Turtle’s subsequent sorrow, Adversary grew stronger over the millennia, until, after Donatello convinced his brothers to go with him into the wilderness of Northampton, they came to slay it. Their journey into the woods beginning as a merely free spirited journey, soon Donatello began to hear the voice of the Great Turtle, telling him to stand against Adversary, the enemy of all reptiles. Donatello declared himself the "Shaman" to oppose the Adversary, though upon being badly beaten in combat by him, realized the Shaman was Leonardo. Leonardo climbed to the place where he waged his final battle with the Adversary and, guided by the Great Turtle, emerged triumphant. The fossil mesozoic eggs scattered across the world broke apart as fetal reptile souls, the Great Turtle’s included, were freed by the death of the Adversary.