Karthon

Naga, a worshiper of Set and a dead king of Lemuria, formed a group of warriors called Questers led by Karthon. The Questers were ordered to find the Serpent Crown and the search went on for decades. 
 
By the early 20th Century, Llyra, a Lemurian mutant, became a high priestess of Set and a close companion to the elderly Naga. Llyra had ambitions of ruling Lemuria and she had manipulated Naga into arranging a marriage between her and his oldest heir, Prince Merro. Karthon the Quester eventually recovered the Crown along with Namor as a prisoner and returned to Lemuria. Naga quickly wore the Crown upon Karthon's return and Namor stood defiant against Naga.

Namor and Naga soon engaged each other in battle while Karthon, observing Namor's nobility and Naga's sadism, was having regrets about serving Naga. Namor was about to be swallowed up by a pit created by Naga when Karthon drew his sword and killed Naga. Namor and Karthon left the Crown on Naga and the creation of the pit caused earthquakes that swallowed Naga and the Crown beneath the ocean floor. Karthon accepted the Lemurians' decision that he become ruler and he vowed to be a proper king. Namor and Karthon, once enemies, continued to be allies. 
 
Several months later, Llyra's elaborate plans, manipulations and abilty to control marine life culminated in a takeover of Karthon's throne. Llyra managed to subdue Karthon and claimed the throne. Several days later, Namor arrived in Lemuria to speak with Karthon about the surface world but discovered Llyra ruling the city. Karthon was in chains and Namor engaged Llyra in battle while she sent some deadly sea creatures after Namor. The creatures were defeated by Namor and Llyra was severely injured in a rockslide caused by a sperm whale under her control. Namor freed Karthon and Karthon returned to being king of Lemuria.