The moon-kami, 'born' from Izanagi's right eye just after Amaterasu was born from the left eye. He is seldom mentioned after this. Despite being the 'brother' of Amaterasu, and perhaps because of the sound-association of tsuki-yomi (?moon-reader) with yomi the land of the dead, he is not popularly worshipped as a separate kami, but was in pre-Meiji times regarded as the gongen of Amida Buddha.
A Popular Dictionary of Shinto. Brian Bocking.