Aeleus

Aeleus was one of the six apprentices to Ansem the Wise, and the original persona of Lexaeus. He appears in Kingdom Hearts Birth by Sleep.

Kingdom Hearts Birth by Sleep
Aeleus is shown guarding the palace of Ansem the Wise. He and Dilan meet Ventus, but keep him from getting inside the castle, telling him to leave before the monsters come out. Aeleus then spots an Unversed, and both guards begin to head after it as Ventus runs ahead of them. As the two move to follow him, Even approaches and openly wonders what will become of the castle if they left their posts. Aeleus begins to argue, but Even assures Ventus could handle it because he is "special". As Aeleus questions this, Dilan recalls their job to guard the castle, and the two return to their positions at the door.

Sometime after Xehanort's defeat, Aeleus is present when Dilan throws Lea and Isa out of the castle.

Between Kingdom Hearts Birth by Sleep and Kingdom Hearts 358/2 Days
About a decade prior to Kingdom Hearts, Aeleus was still one of six apprentices to the ruler and scientist of Radiant Garden, Ansem the Wise, alongside Braig, Dilan, Even, Ienzo, and Xehanort. Worried the Darkness in people's hearts would eventually consume his world, Ansem began performing tests on Xehanort's heart. Eventually, he created a laboratory in his castle's basement for such experimentation. However, Aeleus and the other apprentices had their own intentions for the laboratory, and began conducting inhumane experiments on the human heart and the darkness within it. Such experimentation led to the creation of Heartless. Ansem quickly discovered their secret experiments, and immediately ordered them to stop. One day, after being advised to review their research data by King Mickey, Ansem found that the effects of their experiments had become irreversible.

Eventually, Aeleus and the other five apprentices dabbled too deep into darkness through their continued experiments. Aeleus, along with the others, was consumed by the darkness, producing a Heartless. However, the apprentices all had strong wills, and so Aeleus also became the Nobody Lexaeus. The six Nobodies formed Organization XIII, and banished Ansem the Wise to the Realm of Nothingness.