Mor'du

''"The witch could see the wounded soul behind his bluster. And so she made a spell that offered him a choice: To fulfill his dark wish or heal the family bonds he had broken. Baiting his brothers with a false truce, the prince claimed his kingdom. To the brothers' protests, he stood before them and drank the spell. At that moment, the spell took effect, giving him strength tenfold, but, to his surprise, in the form of a great black bear. Still, there was the spellbreaker she had given him. If he could only choose to mend the bond torn by pride. Instead he accepted the shape of the monster. And defeated his brothers. The prince returned to command his army, but they saw only the beast. They took arms against him. He slew a great many, and the rest fled the kingdom in terror. With the armies of the brothers fractured, the kingdom collapsed into darkness, and the blight of the Great Black, Mor'du, fell across his domain. Desiring power over the bonds of family, Mor'du has wandered endlessly, his soul forever buried inside the scarred and tormented shell." - ''The Witch telling how the prince became Mor'du 

Mor'du is the main villain of the Pixar movie Brave.

Mor'du is a monstrous, 15 feet tall black bear with huge claws, a misaligned jaw, and long, sharp teeth, his body covered in scars and broken weapon hilts and arrows. King Fergus lost his leg in a battle against this bear while protecting his wife and daughter.

However, Mor'du was not always a bear; he was a human prince, who wanted to take over the kingdom he shared with his three brothers, and went to the witch to gain "the strength of ten men", paying with the ring of his house, which bears two crossed axes. The spell he received eventually transformed him into a bear, soon leading to the fall of the kingdom, as on the dawn of the second day, the spell became permanent and the bear side of him overtook his humanity, making him a monstrous beast.

It is revealed in "The Legend of Mor'du", that not only did Mor'du turn against his brothers but he killed them. After gaining a spell from the witch he summoned his brothers to their father's throneroom under the pretense of peace. But he appeared, demanding their surrender. They refused so Mor'du drank the spell, and was transformed into the demon-bear. He slew his brothers in cold-blood and returned to his army to retake command only to find they did not recognize him nor could he speak. So Mor'du's quest for power failed and the kingdom fell to ruin. As for Mor'du, he lost all his humanity as his human mind was forever clouded by the monster he had become.

Mor'du appears three times in the film, though his existance is often remarked on (though none know of his orgin as the Prince.) He first appears at the beginning when King Fergus and Queen Elinor, with their child Merida are on a hunting trip. When Merida fires an arrow off into the woods and goes to find it, the wisps appear and try to lead her with them. From the undergrowth, it's sugguested that Mor'du is watching her. When Merida finds herself back at the camp, her mother begins taking her away, but Mor'du attacks and Fergus with his household guard rushes to defend his wife and child. Though they give the princess and the queen time to escape on horseback, Mor'du shows no fear nor vulnerability to them, even biting the head off a spear when Fergus tries to stab him. As Fergus draws his sword and goads the bear to attack, Mor'du strikes, cutting to black. Later, it is revealed that the sword shattered when Fergus struck the bear and his leg was eaten, giving him a great hatred of the monster.

When Merida shows her upset at having to marry one of the three lords' sons as her duty to the family, Queen Elinor tells Merida the story of four princes (one of which was Mor'du) who were to have the kingdom split for each, Mor'du plunged the kingdom into chaos by wanting to rule over them and be the best of them, suggesting that he waged war against his brothers. When Merida goes to the witch's hut, the Witch takes the medallion of clan Dunbroch as payment and says that a Prince came to her and asked for the strength of ten men. When Merida asks if this changed his fate, the witch confirms it, showing Merida his clans ring, the crossed axes.

Later, Merida and her mother (now turned into a bear) follow a trail of wisps to a foggy ruin, bearing the crossed axes of Mor'du's family. Merida explores, falling after walking on an unsteady piece of rubble. Inside, she finds a throne room very similar to her own family's and a shattered stone carving of four brother, one of the brothers broken from the others. She slowly realizes that the Prince who asked for the strength of ten men indeed had his fate changed, and that man became Mor'du. Mor'du appears, stalking Merida from the shadows and he charges. Merida fires an arrow straight at his head, but the arrow does no damage whatsoever. Merida hurriedly tries to crawl up through the ruins and reach her mother's paw, with the gigantic bear trying to devour her. At the last second, she leaps and just manages to grab her mother's paw in time as Mor'du snarls and snaps after her. Merida and her mother run as fast as they can away, running to the great standing stones and bashing into them a bit harder, making a hairline crack along one of the great menhirs.

Merida realizes she must mend the bond torn by pride (as the Witch said), fixing a tapestry her mother had made of Merida and the family, thereby breaking the spell. However, her mother is attacked by King Fergus and chased to the ring of stones. As Merida rushes to save her mother and change her back, Mor'du stands from the shadows, following her. Mor'du attacks and her father and the lords fight against the bear, but fail. When Merida herself becomes endangered by Mor'du, Queen Elinor attacks, using her claws and teeth to defend her daughter, but Mor'du, proving much older and more dangerous, beats her down with his vast strength. Elinor, seeing the stone they damaged earlier, smashes Mor'du against the stone and damages it more, but is struck down. As Mor'du stalks towards Merida and her injured mother, the stone falls, crushing him.

The bears claws protrude from under the stone, but his death frees the Prince's spirit, who nods thankfully to Merida and her mother before he takes the form of a wisp and disappears.

Trivia

 * Mor'du's name may come from "mortus", the Latin word for "death." It may have also come from "murh deugh", the Gaelic words for "Great Black."
 * Mor'du is the fourth Pixar villain to actually die at the end of his film, after Hopper from A Bug's Life, Syndrome from The Incredibles, and Charles Muntz from Up.
 * Strangely enough, Mor'du bears some resemblance to the bear that attacked Amos Slade and Copper at the end of The Fox and the Hound.
 * Mor'du is the first Pixar villain who never says a word. He is the second Pixar villain to be a bear, after Lots-o'-Huggin' Bear.
 * Mor'du, after he became a monster, was possibly immortal or maybe had longevity, as the kingdom he came from was lost from memory.
 * Mor'du is not a werebear, werebeast creature that can transform into a bear which is also least popular in some Norse mythology. For Mor'du to be a werebear, he would be able to resume human form, and he was cursed forever to live as a monster.
 * His actions were completely opposite from what Merida did. Whereas after Merida tore a rift in her kingdom and near the end of the movie saved it and learned from her actions, Mor'du allowed his selfishness and lust for power to take over him and destroyed his kingdom.
 * Mor'du has similarities to Emperor Nero. He killed members of his family and his selfishness and appetite for power brought his kingdom to ruins.