Leo Akaba
Declan and Riley's father and former owner of the Leo Corporation, Leo is originally a resident of the Original Dimension where he developed the ARC System and incorporated it with Duel Monsters. When Zarc and his four dragons went on a rampage, Leo developed the four En Cards to seal them away. But his daughter Ray stole the cards and use them to splintering their reality, a displaced Leo ends up in the Standard Dimension in an amnesic state. He worked with Yusho to develop the ARC System from scratch before regaining his memories, abandoning his new life to travel the dimensions to find Ray. It only meeting Celina in the Fusion Dimension that Leo learned that Ray splintered herself into four separate girls, establishing Duel Academy and using his students to launch an interdimensional campaign to gather all four of Ray's splintered incarnations. Once Zuzu was captured, Leo proceeds to merge her and her counterparts back into Ray while restoring the Original Dimension. Though his hastiness failed to fully revive Ray, it restored the En Cards which he takes to defeat Zarc like he had planned to do before. But Zarc quickly defeated Leo before giving him the chance to use the En Cards on him. After Zarc's defeat and Arc-V split into four dimensions once more, the remorseful Leo tries to find out what happened to Ray while assuming the worst case scenario that her incarnations have ceased to be. After Yuya defeats Declan, Leo got transported to Pendulum Dimension just as Ray's body started to react. As Zuzu is revived and reunited with Yuya, Leo finally comes into terms with Ray's death and finally accept her passing. Now he counts on Yuya to make the world as 1 through his dueling.