Cob, a powerful sorcerer from Havnor, became consumed by the desire to conquer death. His studies in palnic magic focused on breaching the boundary between life and death, culminating in summoning the dead, including Archmage Nemmerle, from the Dry Lands. This act provoked a confrontation with Ged, leading to Cob's banishment after he refused to cross into death's realm, fearing mortality.

Banished to the Dry Lands, Cob built a fortress from dragon bones. There, he achieved immortality through suicide, tearing a permanent breach between the worlds of the living and the dead. This rupture drained magic and spread decay across Earthsea. Declaring himself "King of Shadows," Cob gained followers in places like Gont and Hort Town, ruling through intimidation and controlling the slave trade to fund his dark arts.

Cob appears with long purple or violet hair, pale skin, and violet eyes bearing triangular markings beneath them. He wears simple purple robes and wields a staff radiating purple light. This androgynous, feminine guise is a magical illusion masking his ancient true form, revealed when his hand is severed. The injury causes rapid aging, exposing an elderly man with gray-white hair and hollow eyes, his corrupted nature evident in animal-like claws. Literary sources variously describe him as tall and long-armed with dark hair and blindness, or appearing in the Dry Lands with white-gray hair and empty sockets.

His personality is cruel and manipulative, driven by a profound terror of death. He rules Hort Town through fear, engaging in slavery and exploitation. Though soft-spoken, he exhibits sudden rage when opposed. He hypocritically values his own life above all others and uses psychological manipulation—exploiting insecurities—to force victims to reveal their true names, granting him absolute control.

Cob commands advanced necromancy, infiltrates dreams, and casts spells inducing fear or rage. He can kill instantly by summoning and crushing a victim's heart, reattach severed limbs, and transform his body into liquid. His breach between worlds neutralized magic across Earthsea, demonstrating power rivaling an Archmage. Dragons feared his immortality and ability to corrupt their primal language.

His downfall began by kidnapping Tenar to lure Ged. He manipulated Prince Arren, exploiting the prince's inner turmoil. After learning Arren's true name, Lebannen, Cob controlled him to attack Ged. During the ensuing battle at Cob's fortress, Arren severed Cob's hand, breaking his magical disguise and accelerating his aging. Cob captured Therru, but she revealed herself as the dragon Tehanu and incinerated him. In the literary narrative, Cob perished when Ged closed the breach between worlds, crushing Cob's physical form with the dragon Orm Embar.