Castamir

He was the great-grandson of King Calmacil of Gondor and was the Lord of Ships under King Valacar and called the Usurper

When King Eldacar succeeded to the throne he rose into rebellion and deposed him in 1437 T.A. (and did great damage to the capital Osgiliath, burning its Dome of Stars)

He was hailed by the people at first for his pure Númenorean blood. But he proved a cruel ruler and the old King Eldacar had no trouble in finding support (one of his most cruel deeds was the execution of Eldacar's eldest son Ornendil[?].

In 1447 T.A. Eldacar came down from Rhovanion[?] and did battle with Castamir at the Crossings of Erui[?] and slew him personally. Although Castamir died his sons fled to Umbar[?] (And their their descendants became known as brutal pirates called the Corsairs of Umbar[?]) and continued the resistance against Eldacar's descendants for 400 years.