毘沙門天 (pronounced as 'Bishamonten' in Japanese, 'Vaiśravaṇa' in Indian) is one of the most popular 'tenbu' (天部, deva) in Japan. Devas are former gods of Hindu mythology which became the guardian deities of the Buddhism.
He has regionally various characteristics and figures. In Japan, he is a warrior god wearing Chinese-style armor, holding a spear and a miniature pagoda (bishamonten's pagoda). In the Chinese folklore, he has an umbrella and a silver mouse.
He is a member of Four Heavenly Kings (Kanji: 四天王) and the guardian god of the northern direction. His another name is 多聞天 (Tamonten, lit. 'Much hearing god').
In the Japanese folklore, he is a member of 'Shichi Fukujin' (七福神, the Seven Lucky Gods).