Rise of the Thrall Lord
The series of battles to combat the rise in power of the Thrall Masters are known as the Thrall Wars. According to the partial records surviving from that time, there were four Thrall Masters that arose to the level of Thrall Lords.
The Death Lord Vanalor had mastery of all creatures of negative energy, and was also known as Lord of the Undead.
The Golem Master Larketh had control of all animated constructs.
The Dragon Master Urekar had power over all draconic creatures, and was also known as Draconus Imperitus.
Above all was the Lord of All Thralls, or the Lord Thrall. Reportedly Lord Thrall was originally a great and good priest named Valgar who had fallen and became a dark Wizard, later slain by ancient heroes. Unfortunately for the world Valgar rose again in the incarnation of the Lord Thrall. It is suspected by some scholars that Lord Thrall had mastery over Demons.
Lesser Thrall Masters and minor Thrall Herders served each of the Lords, usually manifesting some small aspect of their power to dominate creature in their domain.