Ondoher was the 31st King of Gondor and the son of King Calimehtar. He tried, during his rule, to strengthen the ties between Gondor and the Dúnedain of the north. He was slain along with his two sons, Artamir and Faramir in battle with the Wainriders in TA 1944. Because his two sons died alongside him in battle, Gondor experienced a leadership crisis.

Ondoher also had a daughter named Fíriel who wed Arvedui of the North-kingdom. Arvedui was of the line of Isildur and Fíriel was the only remaining child of the King of Gondor, so Arvedui tried to claim the throne of Gondor, but Pelendur the Steward of Ondoher helped to have his claim rejected.

So it was that the crown was then claimed by Eärnil II who had been the victorious captain at the Battle of the Camp. His claim to the throne was agreed upon by all in Gondor because he was of the royal line. His father was Siriondil who was the son of Calimmacil, son of Arciryas the brother of the 29th King of Gondor, Narmacil II.
Encyclopedia entry originally written by Nienna-of-the-Valar