Malkoran the Skeleton King

The boy that would eventually become one of the most feared beings in the Silverlands was once just a frail half-elf born in an age where being of mixed-race was a taboo. Living on the outskirts of their village as social outcasts, Malkoran and his parents eked out what meagre living they could. One fateful night, a group of bandits raided his village and slaughtered everyone, including the boy's parents. He only survived by hiding under the floorboards of their house, staying silent among the spiders and insects crawling over him.
The child wandered the ruins of his village, in shock, until he was discovered by a dwarf named Lorgren, who had come to the village to make use of the corpses left behind. Lorgren initially planned to kill Malkoran, but after seeing an intense will to survive in the boy's eyes, Lorgren instead took him in, teaching him the forbidden art of necromancy. Malkoran took to these lessons immediately, quickly becoming proficient. Unlike Lorgren, whose preferred necromancy spells were that of resurrection, Malkoran instead enjoyed the destruction and withering of lifeforce that he could unleash with necromancy.
Ultimately, Lorgren both grew tired of raising a child and, feeling that Malkoran could learn no more from him, sent the young necromancer out into the world to find his own path. With him, Lorgren gifted an engraved dagger and two of his best undead thralls, a human female named Adia and a tabaxi female named Nimble Veil. Together the three of them would wander the lands, researching, learning and growing stronger.
At some point, Malkoran learned of a concept called "lichdom" in an ancient text he had acquired. The text was vague and offered no hints as to how the process actually happened, but Malkoran was hooked immediately on the idea of becoming an immortal undead. At this point, the only creatures in the world that had become liches were renegade Mindflayers and a handful of dragons, but Malkoran believed that there was no reason that he could not accomplish the same thing if he gained enough power and resources.
Malkoran set himself on doing just that. He posed himself and his thralls as adventurers for hire, and over several years they performed adventurer jobs for money and fame. At first it was the basics: killing goblins, chasing off bandits, hunting an owlbear, etc. Eventually, however, Malkoran managed to kill a young green dragon that was interfering with a separate job of his. The locals found out of his outrageous kill, and his name immediately began spreading. From this point, Malkoran began receiving more advanced and better paying jobs.
After nearly twenty years of adventuring, Malkoran got his big break. He was traveling along the Triboar trail on the way to Norn when he came upon the city being attacked by a blue dragon named Alustrax. He envisioned a pig payout if he killed the dragon and saved the town, so he got involved. Unfortunately, Alustrax fled as soon as he believed he was losing the battle, but the townspeople nonetheless praised Malkoran as a hero. As he rested at the town, Malkoran was approached by a leader of the local lords' alliance who informed him that they believed the attack on the city to be part of a greater conspiracy being propagated by a dragon cult in the region. Seeing yet another grand reward at the end of this difficult road, Malkoran took up the offer to investigate.
This job took Malkoran nearly two years to complete and saw him temporarily allying with a young elf calling himself Swank to accomplish it. The four of them, Malkoran, Swank, Adia and Nimble Veil, would uncover the cultists' plot to assist the Dragon Queen Tiamat herself in escaping Bresylle and returning to the surface. They would ally with dozens of metallic dragons, bring whole kingdoms together and even acquire the help of some Spellbreakers to foil the cultist plot. Tiamat herself would never successfully enter the Silverlands, but killing several dragons involved and powerful mages in the ranks of the cultists allowed Malkoran to grow like he never had before. After the defeat of the head cultist Severin, Malkoran gained possession of a relic of Tiamat: the Mask of the Dragon Queen. A humbled but living Alustrax approached Malkoran and offered him a deal: give him the Mask and let Alustrax add it to his hoard and gain a blue dragon as a permanent ally. Malkoran accepted.
Now that he had gained immense wealth, knowledge and power, Malkoran secluded himself in a cave somewhere in the wilderness and began researching. He eventually discovered that it was a magical item called a phylactery that allowed liches to live forever. They would move their soul into the phylactery, rendering their bodies in a state between life and death and allowing a new body to be created if the original is destroyed. The soul would safely be held in the phylactery, only requiring constant magical sustenance to maintain its grip on the soul. Knowing that the phylactery was the sole weakness of a lich, Malkoran spent decades and multiple iterations to create a flawless and perfect phylactery. This object was actually once another magic item called the Orb of Life, an artifact held by the fey queen Sybille before Malkoran stole it. He took the orb, which was meant to let anything be resurrected, and converted that magic of life into necromantic magic in a shell that was nigh indestructible.
He next began the process of becoming a lich. His research indicated that what was required was drinking a potion and then killing oneself to transport the soul into its new home, but it also implied that the trauma of death affected liches' mental state. All the liches he had read about, while powerful, were much more unhinged than they were alive. He despised the idea of going crazy, and instead attempted another route. After brewing and drinking the necessary potion, he slowly began to starve himself while sleeping more and more, meditating almost exclusively when he was awake. At some point, after Malkoran fell asleep, what he woke up to was not his frail and shriveled body, but one young, healthy and pulsing with magic.
He had succeeded, and dying in his sleep when he wasn't expecting to had eliminated any trauma, keeping his mind intact. This is the birth of the being that would become known as the Skeleton King, a name feared by all who know it. He would give his phylactery to Alustrax, and in a sort of symbiotic relationship, such a powerful magical item in his hoard made Alustrax far more powerful, not only motivating him to protect the phylactery but granting him the means to do so.
In the millennia since his transformation, Malkoran has created a vast underground labyrinth called the Tomb of Gods, and within it continues to push his boundaries and pursue research on life and death. Many come to seek his favor, from fiends to lesser liches. He allows them to remain as long as they are useful, but kills them without hesitation if they displease him. A young elf has even asked for the Skeleton King's patronage to become his warlock, and Malkoran accepted, curious as to what benefits a warlock might bring him. What exactly he is working on remains a mystery, but the two things that are certain are that he will eventually find what he is looking for, and woe to the world when he does.