Ansem, Seeker of Darkness serves as the main antagonist of Kingdom Hearts and the "Reverse/Rebirth" story in Kingdom Hearts: Chain of Memories. He is the Heartless of Xehanort, retaining the dark "guardian" which belonged to his original self. Ansem appears to have characteristics of both Emblem and Pureblood Heartless, and it is unclear exactly which category he falls under.
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, what little shreds of humanity 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 simply cattle for his ravenous Heartless legions. He revers power and knowledge above all things, and despises ignorance.The only times when his voice rises above a cold, monotonous drone is when he is berating Sora for his foolishness, or reveling in his latest triumph. However, the scientific genius of Ansem was blinded by obsession with the darkness. His arrogance ultimately led to his destruction when the door to Kingdom Hearts opened, and his greatest thesis was, in the end, proved wrong.
As Ansem is made from the heart of Master Xehanort, he appears to share most of his personality traits with the elderly Keyblade Master, demonstrated by his choice of words when facing Sora, Donald and Goofy, and his desire to find, open and become one with Kingdom Hearts itself.
Like his Nobody counterpart, Ansem's skin color varies by being depicted as tan in the game to quite dark in official artwork. He shares Xehanort's amber-orange eyes and long white hair, as well as the three spikes on the top and sides of his head, but he lacks Xehanort's bangs.
He wears silver-white gloves on his hands, each with a grey band on the wrist, while the rest of the glove, which has three black buttons lining one side, bells outwards. There is a black pauldron on both of his shoulders, each attached to his coat by two straps. He also wears black pants and black, silver-lined, knee-high boots identical to the ones worn by Organization XIII members. On the Heartless' chest is the Heartless emblem, but it is unclear if this is simply an article of clothing or actually part of him. It seems that it is not part of him, as when Ansem creates the World of Chaos, he loses both of his jackets and his gloves, and the emblem transfers to the World of Chaos. He also grows to a tremendous size and his eyes become completely orange in this form.
Ansem's black leather coat is red on the inside and lined with yellow, and also has a large grey section that covers the lower half and shoulders of the coat. Upon closer inspection, this grey section seems to be attached by several small pins or buttons around the hip and neck sections of the coat, as well as by a belt that wraps around the Heartless's back and attaches to the rim of the coat. This coat is high-collared and completely unzipped, showing the second, shorter jacket the Heartless wears underneath. Ansem's second jacket is white and high-collared much like the outer coat. It is mostly unbuttoned and exposes Ansem's chest before being closed up by three buttons and two belts near the Heartless's waist, only to flare outward again, leaving three buttons undone. When seen cloaked, Ansem appears to be shorter and more crippled.
As Ansem is born from the heart of Master Xehanort his overall appearance is nearly identical to a younger version of Master Xehanort, wearing the elderly Xehanort's attire.