King Leoric, later known as the Black King and ultimately the Skeleton King, was the ruler of Khanduras just prior to the events of Diablo I. He was a devout follower of the Zakarum religion of the Light, and was a great lord from outside the country prior to declaring himself king. Though he was a foreign king, the people of Khanduras eventually grew to respect him for his evident purity of heart and deed. He made his court in the abandoned Horadrim monastery under which Diablo's soulstone secretly lay. (Why the monastery in the game appears as nothing but a decrepit church, and why Tristram remains a little village, is not given an explanation.) However, Diablo's power stirred at the same time, and the Lord of Terror eventually drew the king's archbishop, Lazarus, into the labyrinth under the monastery, where he found the soulstone and was compelled to shatter it. Thus freed, Diablo sought for the most powerful mortal soul he could possess in order to regain his power, and settled for the king's. Leoric found a dark presence trying to intrude into his being, and though he fought it in secrecy, he was not strong enough to banish Diablo (however, Diablo at his current weakened state was not strong enough to fully overtake Leoric, as well), and his mind became twisted and corrupted. As the change began to show in both his appearance and behavior, his own people started calling him the Black King. The Archbishop Lazarus, also fallen under the power of Diablo, did his best to conceal the nature of the change in the king's person, but eventually suspicions among Leoric's advisors grew to the point that he needed a new plan. Thus, he convinced the now delusional king that the kingdom of Westmarch was plotting to take over and annex Khanduras, manipulating him into declaring war, diverting attention as well as sending many troublesome knights into their deaths when the armies of Westmarch inevitably crushed those of Khanduras.

However, Diablo found that a part of the king's soul still fought against him, and that he would still not be able to take full control. Thus he abandoned his attempts to take over Leoric, leaving him broken and crazed as he much more easily took control of his son Albrecht instead. When King Leoric found that his son had gone missing, he went into a rage and had many innocent people executed for kidnapping the prince. He was eventually slain by his own lieutenant, the knight Lachdanan, who returned from the quickly lost war only to find that he, too, was being accused of the kidnapping, and that the king was nothing but a raving madman who set his other warriors upon those returning.