He was the fifteenth King of Gondor from 1015 T.A. till 1149 T.A.
His original name was Ciryaher. He was the fourth and last Ship-king.
His father Ciryandil was slain defending Umbar while besieged.
He began his reign reorganizing Gondor's armies and in 1050 T.A. he openly declared war on the Haradrim and defeated them.
The Haradrim were forced to recognize him as their lord and king. After this victory he called himself Hyarmendacil, meaning South-victor.
Under his reign Gondor reached its greatest extent and power. The passes of Mordor were well guarded so evil found no chance in Hyarmendacil's reign. Nobody dared to contest his power and Gondor was at peace for the rest of his long reign (134 years)
He was succeeded by his lazy son Atanatar II