Scar's song, written by Elton John and Tim Rice, was originally titled "Thanks to Me" and was performed after Mufasa's death. As the development on the story progressed, the filmmakers felt that Scar's song was performed too late in the film. They also wanted to use Scar's number as a build up to his eventual takeover, thus it was renamed "Be Prepared" and featured Scar and his hyenas plotting to kill Mufasa and Simba and rule the Pride Lands.
Scar is heavily sarcastic, frequently replying to attempts at conversation with sarcasm and subtle insults. After taking over Pride Rock, Scar's overall demeanor takes a turn for the worse, becoming somewhat deluded, if not in self-denial, in believing that he is still a logical ruler despite clear evidence to the contrary, apparently being unprepared to confess even to himself that Mufasa was a better king or finding fault in his own leadership. As such, in a dark parallel to Simba's initial idealism to becoming king, he also proceeds to refuse relocating the Pride from Pride Rock despite being confronted with obvious evidence that any surviving animals in the region had fled the premises as well as there being an ongoing drought, not caring if this resulted in the kingdom's, or his own, death. This implied that a large part of the reason why he decided this course of action was simply because he could give that order as king. Even when he is above Mufasa, having betrayed, murdered and stolen the throne from him, he remains sensitive to his brother's mention. It is one of the only subjects that can flare his temper; at the mere mention of Mufasa, he threatens Zazu, assaults Sarabi, and snaps at his own hyena minions. This indicates that Scar suffers from low self-esteem. Even in a position of power, he remains vulnerable to bouts of indecision and insecurity, as he is unable to accept criticism and too stubborn to take the advice of his advisers. Scar is also a hypocrite, as he begs Simba to spare his life due to their family ties despite the fact that he killed his own brother. He also tells Janja not to run like a coward, ignoring the fact that he himself fled from Simba during the battle of Pride Rock.
Regarding his treatment of Shenzi, Banzai, and Ed, he is somewhat harsh with them, as evidenced by his berating them regarding their failure to kill Simba and Nala (even though they only escaped because of Mufasa's timely arrival, which Scar even witnessed himself), and his angrily kicking them out after Banzai made the mistake of mentioning Mufasa within earshot. He could barely tolerate the idea of relying on "idiots" like them. Worst of all, when he realized that they lied to him about Simba's fate, he gives them a glance which seemed to indicate he would deal with them later. Though his remark when meeting them at the base of Pride Rock following his downfall would indicate he views them as friends, it's clear he only saw the hyenas as pawns and it was only as a way of manipulating them, as he earlier tried to place the blame for all his actions on them to save himself from Simba's wrath when cornered at the peak.
To motivate and mobilize the hyenas, Scar promises that under his rule, the hyenas will never go hungry again (a promise he ultimately fails to keep). With their assistance, he engineers a wildebeest stampede meant to kill both his brother and nephew, tricking Simba into waiting in a gorge under the notion that Mufasa has a 'marvelous surprise' for him which is to 'die for." Scar alerts Mufasa, who rushes to Simba's aid. Mufasa manages to rescue his son and ends up clinging to a cliff where he spots Scar and pleads with his brother to help him. However, Scar pierces Mufasa's paws with his claws and, grinning wickedly, throws his brother off the cliff to his death with the taunting words, "Long live the king" instead. When Scar sees Simba is still alive, he places the blame of Mufasa's death on his nephew to make him feel guilty. Simba asks him what he should do and he orders Simba to run away and never return as punishment. Scar proudly watches Simba run from him with a wicked grin, then sends the hyenas to kill Simba, but they fail this task yet again due to Simba escaping into the desert through a bed of thorn bushes much too wide and dense for them to follow him through. Believing Simba will die in the wasteland, the hyenas let the cub go, yet warn him with death should he return.
In "The Scorpion's Sting", Scar sends a scorpion named Sumu to poison Simba on the day celebrating his victory and reclaiming the Pride Lands. Knowing that volcanic ash is needed to remedy the fatal sting, Scar sends his crocodile, jackal, and hyena minions to slow the Lion Guard, accompanied by Makini, down. It is then that they overpower these foes and secure the ash that he finally makes himself known to his great-nephew and his friends. His minions managed to corner the Guard, but Scar underestimated Kion's skills with the Roar which allowed them to escape. Overlooking his defeated army, Scar declares the war has now begun. After his father's life is saved, Kion vows to defeat Scar once and for all.
After finding out his attempt to have Simba (and an accompanying Nala) killed by the hyenas failed, Scar meets with Shenzi and her clan to form an alliance in order to kill him and Mufasa. Scar promises them that the mighty will be able to take whatever they want when they want thus getting the clan to join him. The next day, Scar takes Simba to the gorge in the Pride Lands, saying that to impress Mufasa after getting in big trouble, he should find his roar in the gorge, which all lions do according to Scar. Scar leaves him to practice as the hyenas stampede the wildebeest herd into the gorge, setting the trap as Scar tells Mufasa Simba is in danger. During the stampede, Scar sends Zazu to rally the lionesses to help while he tries to help Mufasa, leaving no witnesses to his plans. After Mufasa rescues Simba, Scar waits as his older brother tries to scale the walls of the gorge and get away. When Mufasa begs him for help, Scar sends Mufasa falling to his death with a swipe of his paw, murdering him instead. Then he tricks Simba into believing Mufasa's death is all his fault, and tells him to run away as the pride will not accept him for slaughtering his father. After Simba flees, Scar orders Shenzi and the hyenas to kill Simba, but unknown to him and Shenzi alike, Simba gets away after he nearly fell to his demise during the escape.
When he tells the pride about Mufasa's death, Scar lies that he did not make it to the gorge in time. Then Scar takes the throne and brings in the hyenas as his enforcers. Afterwards, he personally leads the hyenas to hunt instead of the lionesses so he can show his dominance over the kingdom, resulting in the Pride Lands becoming a wasteland years later due to his desire to kill prey where and when he wants, making the other lionesses unsatisfied. He offers Sarabi to become his queen, but she denies him, citing his greed and selfishness. To corner her, Scar enforces the rule that the lionesses can only eat the scraps from hyenas' foods until she concurs to become his queen. This causes Nala to depart and search for help, resulting in her looking for Simba as Nala manages to leave Pride Rock without getting caught by Scar.
When Simba returns home and encounters Scar after he attacks Sarabi, he goads him into revealing his "role" in Mufasa's death. While Simba anxiously tries to deny that he did not kill his father just as Scar tells him if he is a king or a betrayer, he pushes him into slipping at the edge of Pride Rock afterwards. Just as lighting strikes a dead tree to cause a massive fire in the Pride Lands, Scar cites that Mufasa had the same look in his eyes before he died, before Scar secretly tells Simba that he killed Mufasa. Upon hearing the truth, Simba bites Scar on his mane and pulls himself back up, angrily asking his uncle how he could do this to their family. Scar tries to protect himself by denouncing Simba's sanity, claiming he killed Mufasa and now plans to kill him next, Sarabi however reveals that she overheard Scar talk about seeing the look in Mufasa's eyes before he died, contradicting him not arriving to gorge in time like he told the pride. Scar, realizing too late that he accidentally exposed himself, orders the hyenas to kill all the other lions and Simba as Nala orders the lionesses to fight against the hyenas.
Scar survives the fall and as he struggles to his feet, Kamari, Azizi and several other surviving hyenas show up and surround him. At first, Scar is relieved to see them, saying that they must rebuild their forces if they are to retake what they have lost. Unfortunately, the seething Kamari and Azizi revealed that they overheard his attempt to double cross them when he called them "revolting scavengers" and planned on killing them. Realizing his mistake too late, Scar tries to reason that he was only trying to fool Simba, and promises that together, they will rule the Pride Lands. However, Shenzi coldly tells him that the only true thing he ever said was that "A hyena's belly is never full", indirectly ordering her clan to devour him alive as revenge for using them and selling them out. Cornered and outnumbered, Scar briefly, but vainly attempts to fight back, only to be overwhelmed and devoured alive by the hyenas, bringing his reign to a well-deserved end. After Scar's death, Simba takes his place as the rightful king of the Pride Lands and undoes the damage his uncle had done, thus finally avenging Mufasa and restoring the land back to its former glory. 2b1af7f3a8