Kroak is a Slann. Little is known of Kroak's life, but he is now physically a long dead husk. After his death, he was mummified and placed on a magical palanquin. His spirit, and many others, still remain hovering around his corpse, protecting it from physical harm.
As a member of the Slann, Kroak has many magical powers, including the ability to call comets from space, attack enemies using surrounding spirits's spectral claws and see into the future.