Vaiśravaṇa (Sanskrit वैश्रवण) or Vessavaṇa (Pāli वेस्सवण, Sinhala වෛශ්රවණ) also known as Namtösé in Tibet and Bishamonten in Japan is the name of the chief of the Four Heavenly Kings and, as "chief", an important figure in Japanese Buddhism. Other Mahayana sects don't make a distinction between "chief" and "subordinate" Heavenly Kings.
Mantra = Om Vaiśravaṇa Ye Soha