Ku Y'Leh was a powerful sage referenced in Act III of Diablo II, and involved in the first quest in that act. The player exchanges a Jade Figurine found from any unique monster in the act for a Golden Bird off Meshif. The bird contains the ashes of the sage, Ku Y'Leh, who, according to legend, brewed and subsequently quaffed a potion that would grant him immortality. He was murdered before the potion could take effect and his body burned in the hope that immortality could be derived from his ashes.
The Potion of Life, which Alkor mixes from the ashes, permanently adds 20 to the player's life, suggesting that while Ku Y'Leh may not have achieved the immortality he sought, he still attained some degree of life after death.