Lethean

Long ago, a particular tribe of orcs was visited by an evil fiend who seduced them with promises of power. Promising them with “blessed waters” to enhance their might, the orcs eager drank water taken from an abyssal river which erases the memories of all who consume its waters. Once their memories were gone, the fiend enslaved their for generations. Eventually, the tribe rebelled, slew the fiend, and escaped, but they were forever changed by the experience. Due to being fed the abyssal water for generations, leathean orcs suffer from reduced mental capacity, but in exchange, they gain access to powerful akashic abilities.