Who is Ansem the Wise?
The man who called himself "DiZ" and dressed his face in bandages to conceal it, now revealed to be none other than Ansem the Wise. The true Ansem once studied hearts and the Heartless, but soon ceased his research for fear of disrupting the order of the worlds. But his apprentice Xehanort betrayed him, robbing Ansem of his discoveries and pride.
What did Ansem do for the city of light?
From a time before the Unversed began invading the Realm of Light, Ansem was the king of Radiant Garden, the "city of light". He governed the Radiant Garden in peace and studied ways to make it safer with his five apprentices, Braig, Dilan, Even, Aeleus, and the orphan Ienzo.
Why was Ansem banned from the Dark World?
Ansem was eventually usurped by Xehanort, who lead Braig, Dilan, Even and Aeleus in banishing him to the Dark World, so they could continue their research without his interference. For some time, Ansem remained in the empty realm, constantly writing his own reports in order to maintain his sanity.
How did Ansem get the corridors of Darkness?
In one of his reports, Ansem stated that after he discovered his new-found powers, he gained the ability to use Corridors of Darkness for travel, though he admits that it was difficult to control initially. This was shown after Riku defeats Roxas; Ansem arrives shortly to take Roxas with him.