Once a holy cleric, Aldrich forsaw an age of deep sea, and through his visions was able to reach a level of dark that was inaccessible to humanity. There he developed a habit of consuming humans, growing more and more powerful he found the cannibalism delightful. The Church of White chose him as the next lord of Cinder, not out of his worthiness but for his power. Most who worship the deep as he did became corrupted, but Aldrich retained his sanity. His physical body however was not immune, collapsing into a polluted mass of abyssal sludge.
After his revival as one of the lords of cinder, he neglected to take his throne. To him it was inevitable the world would be engulfed in darkness. It was then that he sought to devour the Old Gods, and took control of Irithyll. The Pontiff of Irithyll was forced grant Aldrich access to Anor Londo and surrender Gwyndolin, whom Aldrich is consuming when the Ashen One arrives.