Bosatsu is the Sino-Japanese translation of the Sanskrit term "bodhisattva," which refers to saintly entities in the Buddhist tradition who, even though having reached the highest stages of enlightenment in their current existences, vow to postpone entry into nirvana (the state of ultimate, existence-transcending enlightenment) in order to help all living beings and lead them toward more enlightened states. Originally, the term referred only to the Historical Buddha before his entry into nirvana (or during his previous existences), but with the development of the Mahayana tradition, a number of other spiritual entities appeared, including (in their Japanese pronunciations) Miroku, Kannon, Seishi, Monju, Fugen, and Jizo, who are also considered to have bodhisattva status.
As Buddhism spread among the common people, the term "bosatsu" was sometimes applied to very respected persons of unusual virtue such as Gyoki Bosatsu during the Nara Period and Kosho Bosatsu during the Kamakura period. And reflecting the once-popular notion of convergence between Shinto and Buddhism, there was once the custom of giving the bosatsu title to certain Shinto deities, as in the case of Hachiman Daibosatsu.
Unlike the Historical Buddha and other nyorai, images of bosatsu commonly wear jeweled crowns on their heads and have other ornamental accessories attached to their bodies, the roots of which are said to be traceable to aristocratic fashions in ancient India. Compared to nyorai images, bosatsu images show a greater variety of pose and attitude. Many are artistically superb and create a human-like feeling of intimacy.