Hittite king during the New Kingdom (reigned c. 1286–c. 1265 BC); he came to power by overthrowing his nephew Urhi-Teshub (Mursilis III).

The events of Hattusilis' accession are known from his autobiography, a remarkable document designed to justify the new king's actions. The change of rulers seems to have caused no serious upheavals in the political fabric of the empire, perhaps because Urhi-Teshub was both inexperienced and unpopular. Except for some military action in the Arzawa lands in southwestern Anatolia, the regime of Hattusilis and his influential wife, Puduhepa, was generally one of peace and prosperity. Together they reoccupied the old capital at Hattusa (now Boğazköy, Tur.) and instituted various constitutional reforms. Common danger resulting from the growing power of Assyria led to an increasingly close entente between the Hittite Empire and Egypt, formalized by the peace treaty of c. 1286 BC and sealed later with a dynastic marriage between Hattusilis' daughter and the Egyptian king Ramses II. Hattusilis was succeeded by his son Tudhaliyas IV.