Robed Figure is Terra-Xehanort's Heartless and the original form Ansem, Seeker of Darkness had prior to possessing Riku. He was created when Terra-Xehanort, masquerading as Ansem the Wise, reawakened his sleeping memories and willfully split his heart from his body. Due to him doing this of his own will he managed to retain his memories in his new existence, and gained the ability to control the other Heartless. He also gained the ability to time-travel due to having been reduced to just a heart.
Ansem attacked the Realm of Light using the Heartless, intending to have them consume the hearts of every world and lead him to Kingdom Hearts. He eventually came across a boy named Riku which he decided to possess thus allowing him to have a proper body again.
Before Kingdom Hearts Birth by Sleep
On a quest from his original persona, Ansem travels back in time to when Xehanort lived on the Destiny Islands. Ansem entrusted his younger self with the mission to gather ten vessels to house fragments of Master Xehanort's heart to create the Organization XIII so that they could create the χ-blade and restart the legendary Keyblade War. To accomplish this, Ansem gave Xehanort the power to travel forward into the future. Once his mission was done, young Xehanort would lose his memory of the event, although the subconscious memory would lead Xehanort to become a Keyblade Master. Ansem himself remained on the Destiny Islands until the time the Destiny Islands were destroyed, ensuring a version of him existed across time to allow his younger self the ability to travel to any time period.
Between Kingdom Hearts Birth by Sleep and Kingdom Hearts
Terra-Xehanort, at the time using his king's name, "Ansem", willingly gave his heart to the darkness in the pursuit of knowledge, creating both his Heartless and his Nobody, Xemnas. His Heartless was able to retain its selfhood for uncertain reasons, though it was believed by the first Ansem that this was due to Terra-Xehanort's willing abandonment of his heart. The self-styled "Seeker of Darkness" and the legions of Heartless at his command continued Xehanort's pursuit of knowledge in the belief that it lay with darkness, and stole countless hearts from both humans and worlds in their search for their ultimate goal, a legendary repository of tremendous power and knowledge known as Kingdom Hearts. To reach this heart of all worlds, Ansem would need to open the Final Keyhole, and to do that, he would need the Princesses of Heart to complete it first. He also realized that he needed to locate and neutralize the wielder of the legendary Keyblade, to prevent them from saving the worlds from his Heartless. He detected a power within Kairi, a Princess of Heart living within Radiant Garden, linking her to a guardian of light, which he misidentified as an innate connection between Princesses and Keyblade wielders. In truth, the power within Kairi was the charm Aqua had placed upon her, with much the same effect—when he cast her loose in the Ocean Between, she was naturally drawn to Sora and Riku on the Destiny Islands.
Ansem, after nine years of being a Heartless, appears in a brown robe at the Destiny Islands Keyhole before the world's fall into darkness, insulting Sora's ignorance of what was to come, and completely ignoring Sora's questions. He then vanishes when Sora's back is turned.
It would later turn out that Ansem was not insulting Sora for not knowing what was about to happen that night, but what would happen in the future. The future versions of Sora and Riku from two years from then would return to the past right before the destruction of Destiny Islands as part of their Mark of Mastery exam to wake the Sleeping Worlds. As part of Master Xehanort's plans, Ansem was there to allow himself and the other members of the real Organization to follow the duo and make one of them another vessel for Master Xehanort's heart. To separate them to better the Organization's chances, Ansem creates a phantom of Ursula to attack them. After its defeat, Ansem watches as the two enter the Sleeping Worlds, noting that he has connected this world to them.
After the destruction of Destiny Islands Ansem appear before present day Riku and opens a Corridor of Darkness for him which leads to Hollow Bastion.
Seeing the same kind of lust for power that he had once seen in Terra coming from Riku, Ansem appears before him following his battle with Sora. Riku is confused over why the Keyblade left him, to which Ansem explains; only a strong heart can wield a Keyblade. He tells Riku that to become stronger, he must open his heart to the darkness and let his entire being become one with it. Riku complies, opening himself to the darkness. However, Ansem uses this to posses Riku, regaining a body.
Ansem as the Robed Figure appearance in one of Roxas's dreams.
The Robed Figure was little more than a wandering heart and could only appear as a figure in a brown hooded robe. This robe has two dark brown straps crossing over his shoulders and chest with five metal studs lining either strap. Due to his lack of a body, he appears much shorter and crippled in this form and wears the robe's hood up that hides his face.
Ansem is, thus far, one of only three Heartless with human-level intelligence, the others being Sora's Heartless and Scar. His knowledge of the worlds and hearts shows that Xehanort's keen intellect has survived the transition into a Heartless. However, the few shreds of humanity which remained in the researcher have been obliterated. Ansem is cold, calculating, and utterly ruthless. He treats people and their hearts as either tools to be manipulated and disposed of, or as cattle for his ravenous Heartless legions. He reveres power and knowledge above all things, and he despises ignorance.
As a Heartless, Ansem has control over darkness, which he can use to attack others, steal hearts, and create Corridors of Darkness. He can also possess other beings, and has command over the Guardian. Due to lacking a body, he is also capable of traveling through time.
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