Ninigi-no-Mikoto (瓊瓊杵尊) (also Ame-nigishi-kuni-nigishi-amatsuhiko-hiko-ho-no-ninigi-no-Mikoto) is, in Japanese mythology, the son of Ame no Oshihomimi no Mikoto and Takuhadachiji hime no Mikoto, and grandson of Amaterasu, who sent him down to earth to plant rice there. He was the great-grandfather of Emperor Jimmu. His name also appears as Ninigi (瓊瓊杵).
Amaterasu sent him to pacify Japan by bringing the three celestial gifts used by the emperor: the sword Kusanagi, the mirror Yata no kagami, and the jewel Yasakani no magatama. These three gifts signify that the emperor is the descendant of Amaterasu herself. The account of Ninigi no Mikoto being sent to earth appears in the Nihon Shoki.
References
Ninigi-no-Mikoto Wikipedia(Text) CC BY-SA