Scar is the main antagonist in The Lion King. In the Broadway musical, Scar's role is expanded upon with the song "The Madness of King Scar". In it, Scar begins doubting his reign, fearing that he might be losing the respect of the lionesses and that he needs a queen. He attempts to seduce Nala when he chooses her as his queen, promising to share the throne with her, but she rebukes him by scratching his face. The musical also implies that he might harbor some guilt for murdering Mufasa, as he mentions that Mufasa's ghost kept on haunting him. The musical also implies that his main motives for wanting to become king was due to neglect that he suffered while he was young, especially in comparison to Mufasa.
According to A Tale of Two Brothers, Scar was given the name "Taka" which is Swahili for "dirt" or "trash" as the younger son of Ahadi and Uru. His older brother Mufasa was chosen to be king over him, a decision which caused Taka much sadness and distanced him from his father and older brother. Over time, Taka came to resent Ahadi for favoring Mufasa and for choosing kingly duties over spending time with his sons.
One day, Taka went on a patrol with his father and older brother. While patrolling the Pride Lands, the three ran into Rafiki, a traveling baboon who was being plagued by the hyena trio until he was saved by Ahadi, alongside his two sons Mufasa and Taka. After the departure of the hyenas and talked about Rafiki's mission, Ahadi welcomed Rafiki into the Pride Lands and let him spend the night at Pride Rock. After Taka commented that they should have let the baboon die, when Mufasa stayed by his father's side throughout the ordeal, Taka wandered off, feeling unconcerned with his father's doings.
Later that night, Taka set a cobra on Mufasa, hoping to kill his brother in his sleep, but Rafiki thwarted the plan. The following day, after the attempted murder Ahadi had planned to take his sons out hunting, but a group of angry Pridelanders had stalled him, and he was forced to cut the hunting trip short a change of events which that does not settle well with Taka. Though Mufasa understood why his father had made that decision, Taka reacted with outrage and accused his father of always finding other things to do when they were supposed to spend time together. In answer to his son's protests, Ahadi attempted to explain that Mufasa understood the pressures of ruling a kingdom, but Taka's temper only flared, and he accused Ahadi for favoring Mufasa. Despite the young lion's animosity, Ahadi decided to pursue his kingly duties, by leaving Taka alone to hunt with Mufasa.
Before the hunt, Taka plotted with the hyenas to get his brother in trouble with Ahadi so that their father might have second thoughts about Mufasa becoming king. Once he agreed with the hyenas he lead Mufasa to a water hole, where an antagonist buffalo named Boma was hogging one of the only water sources left after the start of the drought, and when Mufasa attempted to reason with Boma, Taka roars with an ultimatum: and told Boma that, he's enforcing the Kings orders, telling him if he doesn't listen to him he will challenge Mufasa to a fight. Boma becomes enraged when he tricked Mufasa into angering him. When the buffalo began to chase Mufasa, Taka only laughed at his brother's fear until Boma's herd began to attack the young lion giving him his scar.
Just in time, Ahadi arrived to stop the attack and an unconscious Taka was taken back to Pride Rock, where Rafiki cared for him until he was patched up enough to speak. And Taka's eye was wounded from the buffalo herd and told him that it will never heal and he will carry a scar with him for the rest of his life. Once recovered, Taka was told by his father, that the scar he earned will serve as a reminder of his recklessness. When Mufasa asked his brother why he made Boma angry, Taka only admitted that he had wanted to embarrass Mufasa and get even with Ahadi for breaking his promise, and Ahadi warned his son, to keep his anger at bay. At first Taka was angry, but then Taka at last accepted his father's words, and asked to be called "Scar" from now on.
In his youth, Scar was tasked with leading the Lion Guard, and was gifted with a powerful roar called the Roar of the Elders by the Great Kings of the Past. Which when used he summoned the Great Kings of the Past, to roar along with him. However the power got to Scar's head, and he believed that with this power he should be the king instead of Mufasa. So planned to dethrone Mufasa, by using the Roar of the Elders. When the rest of the Lion Guard refused to help aid him in his plot, Scar destroyed them and thus lost his powers as the Roar of the Elders was not meant to be used for evil. In the years that followed the Lion Guard's downfall, Scar focused his life on striving for Mufasa's throne and continued to plot schemes with the hyenas to rule the Pride Lands.