The Epic of Sundiata, the Lion King of Mali, is a (presumably) fictitious account of how the ancient ruler, Sundiata Keita came to unite the Mandes nations and found the Malian Empire. Due to the nature of the original as an oral tradition, there is no singularly "correct" version of the story, though they all hit the same major beats.
There once was a Mandinkan king named Maghann Kon Fatta, who was wed to many wives, the head of which was his first wife Sassouma Berete, whose son Dankaran was in line to be king after his father.
One day, hunters from Do sought an audience with the king and gave to him a new wife named Sologon Kedjou, who was homely but said to have possessed the spirit of the buffalo. Maghann's griot-- friend, adviser, musician, storyteller, historian, and sage-- foretold that the son of the buffalo-spirited woman and the lion-spirited King would become a great ruler, so Maghann accepted Sogolon as his newest wife.
Sassouma became jealous, and she and the other wives mocked Sologon mercilessly for her ugliness. When Sogolon gave birth to the crippled boy Sundiata, none believed he could become king; the boy did not speak through his childhood, and he had to drag himself over the ground, or else rely on others to carry him. Sassouma and her son laughed off the idea that Sundiata could ever replace Dankaran as king.
For seven years, Sogolon tried to heal her son with potions and herbs, all to no avail. Despite his apparent weakness, when Sundiata was seven years old, his father called an audience with him. Maghann offered Sundiata a young man, Balla Fasseke, the son of his griot to become Sundiata's griot. For the first time in his life, Sundiata spoke out, and he said with grace and fluency that he accepted Balla as griot and friend. Maghann, thrilled to hear his son speak and finding him with a clear mind, began preparing him to rule, teaching him the ways of leadership and statecraft, while Balla was trained in the ways of the griot, and the two grew up together in friendship and wisdom.
However, when Maghann died a few years later, the council of elders paid no heed to his dying wish and, at Sassouma's urging, made Dankaran king. Sassouma once again began mocking Sogolon and her crippled son. Sogolon, heartbroken by the death of her husband, the injustice to her son, and the uncertainty of her family's position in the court, wept.
Sundiata, seeing his mother so desolate, ordered Balla to bring him an iron rod from the smith. When he received it, he pried himself from the ground, bending and breaking the rod, and when it snapped in half and fell away he was left standing on his own. Word spread quickly, "There has been a miracle! The crawling lion can walk!"
Sassouma, fearing that Sundiata would challenge Dankaran for the throne, began plotting against him in earnest.
Despite what Sassouma feared, Sundiata did not challenge his half brother, and instead devoted his time to becoming a great hunter.
In one version of the story, Sassouma seeks out the aid of a group of witches, commanding them to attack Sundiata with magic. Unfortunately for her, because his heart is pure and full of only kindness, the witches can do nothing to harm him; their magic can only cause ill to those who already carry ill within them. She commands that they find some way to anger him and corrupt his spirit so that they can work their magic.
Knowing how much he cares for his mother Sogolon, Sassouma sends the witches to destroy Sogolon's garden. When Sundiata catches them stealing, instead of getting angry, he gives them his mother's herbs and treats them with undeserved kindness. The witches return to Sassouma and tell her there is nothing they can do to the boy.
In another version, Sundiata's younger sisters are gifted in the ways of magic themselves and protect him from the witches' attacks.
Furious and paranoid, and finally seeing that what a skilled griot Balla was becoming, and how loyal he was to Sundiata, Sassouma decided to separate the two, thus cutting away Sundiata's support he would need for ruling. She sent Balla and Sundiata's half sister, Nana, to the kingdom of Sosso, which was ruled by the wizard-king Sumanguru. It was a trap; once Balla and Nana were there, Sumanguru saw what skill Balla had as a griot and vowed to keep him in Sosso forever.
Finally realizing what a threat Sassouma and Dankaran were, Sogolon took Sundiata and his two younger sisters away into exile. They traveled far and wide across many kingdoms, and in most places they were shunned for fear of what Dankaran and Sassouma would do to any neighbor who gave them shelter. However in many places they were aided briefly before being sent on their way, and finally the family found peace in Mema, where the king Moussa Tounkara takes them in. Moussa was impressed by Sundiata's skill as both a hunter and a statesmen and he took him under his wing. Sundiata soon proved his worth on campaigns with the king to defend Mema from the mountain tribes that harried the outskirts of the kingdom. After several years the king of Mema, having grown to care for Sundiata as a son and having no heirs of his own, appointed Sundiata his heir and second in command.
Eight years after leaving Niani, a messenger comes to the Mema court searching for Sundiata. In the time he has left, Sumanguru the sorcerer-king and his armies have taken over several kingdoms, and is waging war on Sundiata's home. Both Sassouma and Dankaran fled in fear, leaving the Mandinka people vulnerable and leaderless.
Sundiata immediately prepared to return home, and the king of Mema lent him half his army. Sudniata journeyed home, stopping at all the countries that had both welcomed and cast him out before, all of whom offered him any aide they could to help him defeat Sumanguru. Just as he reached home, his old friend and griot, Balla Fasseke appeared by his side. Balla explains that while serving Sumanguru he learned the wizard's weakness; an arrow with a white rooster's spur attached-- a magic charm that will rob Sumanguru of his magic. He escaped as Sumanguru went to wage war and he has been searching for Sundiata ever since. In many versions, Balla also steals an instrument called a balafon, which Sumanguru used to cast most of his magic.
Sundiata took the arrow and he lead his armies to Kirina, where a great battle took place between the armies of the many nations of Sundiata's allies and the army of Sumanguru. Sundiata struck the final blow, firing the arrow and piercing Sumanguru in the shoulder. Sumanguru, feeling the magic drain away from him, fled into the mountain, where he used the last bit of magic he had to transform himself into stone to avoid true death.
Without their leader, the wizard-king's army was quickly subdued. Sundiata was given his rightful title as king of the Mandinka people, and the leaders of the other kingdoms who had aided him vowed their loyalty to him, thus forging the Empire of Mali, and he became king of kings, Mansa Sundiata Keita, the Lion King of Mali.
I retold the versions of the story I read as a kid the the old Holt Literature textbook, as well as other places, but here is a much MUCH longer and more in-depth version.