40,000 years ago, Orin was the King of Atlantis, and the elder brother of Shalako, their religious leader. To protect his people from hostile outsiders, Orin erected a dome around the city of Poseidonis. While that saved Poseidonis from destruction when Atlantis sank into the sea shortly thereafter, Shalako claimed that the very actions of his brother had angered the gods and caused the cataclysm. This was the start of a never-ending cycle of brother fighting brother in the Atlantean Royal Family. While Orin created a serum that allowed his people to survive underwater, Shalako took a faction of the Atlanteans with him to found the underwater city of Tritonis. Orin lived and ruled Poseidonis for hundreds of years, but was ultimately killed by Shalako's son Dardanus. He was survived by his wife Narmea and succeeded as ruler by his daughter Cora.
In modern times, a descendant of Orin was born in Poseidonis. Seeing his blond hair as a curse, the Atlanteans abandoned him on Mercy Reef. However, the child survived and would grow up to become King Orin II, a.k.a. Aquaman. During a recent adventure in the past, Aquaman met his namesake ancestor in a battle against Kordax.