The first Emperor of Japan in the 7th century was Emperor Tenmu, who reigned from 673 to 686 AD. He is recognized for unifying the country and implementing a series of significant reforms that contributed to the establishment of a centralized government. His reign helped lay the groundwork for the future imperial structure of Japan and marked the beginning of the Nara period, during which Buddhism and Chinese cultural influences flourished. Emperor Tenmu's leadership was instrumental in solidifying the imperial line and enhancing the political landscape of early Japan.