Thelon, an elf leader of Havenwood, faced a dying forest as Sarpadia's climate changed. Desperate to keep his people alive, Thelon turned to the Order of the Ebon Hand to learn the secrets of thrull creation. He then applied this knowledge to create thallids, plant-based creatures that the elves used as both servants and food. The thallids proliferated and were eventually the elves' downfall. It's said that when the Sarpadian Empires fell, only the thrulls and thallids were left alive on the continent.
"As the climate worsened, some Thelonites turned to fertilizing with fresh blood in an attempt to keep Havenwood alive and growing." -Sarpadian Empires, vol. III (Thelon)
"The sight of my thallids still thriving is a bittersweet welcome to this cold waste." (Thelon)