Thutmose I (thŭt´mōz, tŭt´–) or Thothmes I (thŏth´mēz, tōt´mĕs), d. 1495 BC, king of ancient Egypt, third ruler of the XVIII dynasty; successor of Amenhotep I. He became king c.1525. In a great campaign he subjugated the valley of the Nile up to the Third Cataract (below the present Dongola). Syria occupied his attention, and he at least temporarily subdued the country as far as the Euphrates River. He was succeeded by his son Thutmose II.