Scar

Scar is Simba's evil uncle. Scar was always jealous of his older brother Mufasa, and always tried to hurt him so that he could become king of the Pride Lands.

Kingdom Hearts II
The Lion King (1994)

Simba's evil uncle and brother of Mufasa.

''After Mufasa's death and Simba's disappearance, Scar became king of the Pride Lands and used the hyenas to do his dirty work. Scar hasn't taken care of the Pride Lands, and almost all the animals have been forced to leave.''

Kingdom Hearts II
Kingdom Hearts II lays host to the story of Scar's rule over the Pride Lands. Scar teams up with Pete to control the Heartless as a way to rule the kingdom with discipline. Scar is the King of the Pride Lands, and when he first meets Sora, Donald and Goofy at Pride Rock, he wishes to eat them, as there is little food in the Pride Lands because of his rather shoddy treatment of them. The trio escape and convince Simba to return to Pride Rock.

When this occurs, an overconfident Scar reveals the truth about Mufasa's death, enraging Simba and prompting him to chase after his murderous uncle. While Sora, Donald, Goofy, Timon and Pumbaa hold off the Hyenas, Simba fights Scar at the top of Pride Rock. Sora and co. arrive in time to watch Simba throw the pretender to the throne off the cliff, but Pete arrives and tells them that because of the anger and jealousy within his heart, Scar has become a Heartless. A battle ensues as Scar climbs back up to the peak, with Sora and the gang victorious.

In the second visit to the Pride Lands, Scar appears as a dark ghost which haunts Simba, taunting him and saying he will never be a true king. The ghost lives as long as Simba has doubt in his heart. He eventually defeats this doubt by battling the Groundshaker, and the ghosts disappear.

Trivia

 * After Scar becomes a Heartless, instead of turning into a common Heartless, he retains his form, like Clayton and Shan Yu. This backs up the theory that if a being willingly hands his heart over to darkness, they can retain their form (such as Xehanort's Heartless).
 * If the above theory is true, it's possible that Scar's Nobody and/or the Heartless counterparts to the members of Organization XIII could be fleshed out in future Kingdom Hearts games.
 * Scar's skin can be seen in the Disney film Hercules (1997) in the Scene where Hercules' portrait is being painted onto a clay jar.
 * Scar is, so far, the only Disney character to have actually turned into a manifestation of Darkness (note, however, that Scar's Ghost is not a Heartless).