DiZ
DiZ is a character from the videogames Kingdom Hearts: Chain of Memories and Kingdom Hearts II, and the original Ansem. He experimented on Xehanort, who was believed to be Ansem in Kingdom Hearts and Kingdom Hearts: Chain of Memories.
Backstory
The original occupant of Hollow Bastion, Ansem was a respected sage and king of the Radiant Garden. He believed that darkness could spread into hearts, no matter how pure, and could take control and swallow the heart. In order to bolster defenses against the darkness threatening his world, he researched the darkness and its relation to the heart, using inhumane experiments to discover knowledge by using his own lab assistants, whose Nobodies would later join Organization XIII. This resulted in his discovery of the creatures which he named the "Heartless", and began to study, writing down his findings and ideas in his report. One of his test subjects was Xehanort. Eventually, he found his way into the deepest part of his castle and discovered a huge mass of energy within the 'heart' of his world.
Upon discussion with the off-worlder, King Mickey, Ansem immediately ceased his experiments realizing the danger. However, the damage was already done. Xehanort, under the impression that he was truly Ansem, continued his teacher's experiments, including using a machine to artificially create Heartless with his crest. As a result of Ansem's research for omniscience, Xehanort used the Heartless to ravage Hollow Bastion under the notion that he was Ansem and sought to gain the knowledge of the mysteries of the universe his creator once desired. This led to the discarding of his body and the creation of Xemnas. Because of the horror he had unleased, Ansem was forever shamed by his creation's actions and hid out of self-loathing and guilt until he decided to take matters into his own hands and erase his mistakes. From that point on, Ansem took on the name of DiZ and wore concealing red robes with his face covered in red bandages except for his right eye and mouth until he had cleared his name.
Chain of Memories
In Reverse/Rebirth Mode for Kingdom Hearts: Chain of Memories, Riku found himself in a completly white place. Riku heard a voice and is presented the option of going back to sleep or going back to the world and face the darkness. Riku chooses to leave and ended up in Castle Oblivion. There, the voice guided him, reminding him of how he threw everything away for the power of darkness. The voice finally appeared up as the Ansem Riku knew in Twilight Town. Riku quickly determined he is not Ansem, and the entity reveals himself as DiZ
DiZ explained that he wanted Riku to make a choice after meeting Naminé. After defeating the Riku Replica, Riku received Naminé's offer: she can lock the darkness inside his body and allow him to forget the darkness in him. Riku chooses, of course, to fight it. After completing Twilight Town, Riku meets up with Mickey who revealed that he somehow knew DiZ. DiZ explained that he would watch and see if battling Riku fighting "Ansem" was his right choice.
After defeating Ansem, Riku and Mickey walked down a path away from Castle Oblivion, wearing Organization XIII's coats. They met DiZ at a fork in the road who offered Riku yet another choice: take the road to light or the road to darkness. Instead, Riku chooses the middle road. DiZ asks, "You mean the twilit road to nightfall?" to which Riku replies, "No...The road to dawn."
Kingdom Hearts II
DiZ's role in Kingdom Hearts II was to generally to destroy Organization XIII, while at the same time helping Roxas meet Sora with the help of Riku, Namine and King Mickey.
At the end of the game, DiZ reveals his plan to seal away Kingdom Hearts before Xemnas would use it with a machine that he invented.
DiZ died during the process, telling Riku that he's leaving the rest up to him and asking King Mickey's forgiveness for his foolishness.