Aldamir was a Dunedan and the twenty-third king
of Gondor. He
lived at the time of the Kin-strife (the civil war in Gondor), and was
the second son of Eldacar, son of Valacar.
Aldamir was slain in the in the battle at Umbar (against the Corsairs and Haradrim), and was suceeded by his son, Vinyarion.
Vinyarion took the name Hyarmendacil II, and avenged his father's death by taking Umbar from the Haradrim.
Reference: The Return of the King