He is the son of Anárion.
It is doubtful whether he was King by right for his young cousin Valandil, King of Arnor would have legally been his overlord.
But the people of Gondor didn't resist his claim on the throne and King Valandil made no serious attempts to regain control over Gondor.
He died in 158 T.A. and was succeeded by his son Cemendur.