Madara Uchiha (KH:RTD)

Madara Uchiha is the founder of Akatsuki and the strongest of the Uchiha Clan.

Leader Of The Uchiha
Decades before the start of the series, Madara grew up in constant competition with his younger brother, Izuna Uchiha, who were both known as the most gifted members of their clan. Their competition led to both gaining the Mangekyo Sharingan, and, with it, they were able to take control of the Uchiha clan, Madara acting as its leader. Even by his clan's standards, Madara's chakra was unusually strong. Under his leadership, the clan conquered all they came across, but, over time, he began to lose his sight because of the Mangekyo Sharingan. To regain his vision, he took his brother's eyes (an act Madara said his brother had consented to), allowing him to obtain an "Eternal" Mangekyo and continue to lead the Uchiha to prosperity.

Akatsuki
The Uchiha clan died out and Madara founded Akatsuki. While walking through the streets of Traverse Town he found 2 young boys eating nothing but a loaf of bread. He saw potential in the boys (Who turned out to be Uchiha Clan members) and decided to recruit them to his group of mercenaries. He went to the Radiant Garden 4 years later and confronted Sephiroth. He easily defeated him and Genesis appeared to greet Sephiroth as "Friend".

He taught the two young boys, Sasuke and Itachi to use their Sharingan and to use dark energy to create Dark Keyblades.