In the Manga

The mysterious "Doctor" is a highly talented scientist who is interested in nanomachines. His desire to know reaches the level of psychosis, and he cares little for any lives he may take or destroy in his pursuit. He reattaches Train's right arm after it is severed by Creed's Imagine Blade, at Creed's request, and later captures Eve, intending to dissect her. The Doc's Tao Power is called "Warp World," and it allows him to literally create an alternate world where everything he imagines becomes reality. He can also pull memories from the minds of those trapped in the Warp World, and bring those into reality as well. He has no relation with Dr. Tearju or the creation of Eve or Eden in the manga.

In the Anime

The Doctor appears to be the same as in the manga. He never reattached Train's arm (since that scene never happened in the anime) nor did he capture or attempt to dissect Eve. However, he plays a major role in the Eden project, as he is the one who controls Adam's actions towards uniting Eve with Eden, by simply playing cue-ball. After talking to Dr. Tearju through his computer screen, where it is revealed he was the one who retrieved Eden's data that Dr. Tearju tried to destroy, he participates in the battle between the heroes and the Zero Numbers, where he transforms himself into a monster (although only his transformation is seen in one scene, circumstantially, and is never seen in full-body). He looks quite similar to Kilnorton from The Law of Ueki minus the ponytail.

Source: Wikipedia