Mikao Usui (August 1865 – 9 March 1926, commonly Usui Mikao in Japanese) was the founder of a form of spiritual practice known as Reiki, used as a complementary therapy for the treatment of physical, emotional, and mental diseases. According to the inscription on his memorial stone, Usui taught Reiki to over 2000 people during his lifetime. Sixteen of these students continued their training to reach the Shinpiden level, a level equivalent to the Western third degree, or Master/Teacher level. Usui died on 9 March 1926 of a stroke.

Usui was born on 15 August 1865 in the village of Taniai in the Yamagata district of the Gifu Prefecture, Japan, which is now located near present day Nagoyo.

Usui was influenced by Shintoism, the traditional faith of the Japanese people prior to contact with China. Shintoism focuses on the kami, which are gods in the forms of birds, animals, mountains, trees and people. An 18th century scholar, Motoori Norinaga (1730–1801) said, “According to ancient usage, whatever seemed strikingly impressive, possessed the quality of excellence, or inspired a feeling of awe was called kami”. Usui was known to use jumon – spells or incantations in his teachings, derived from Shintoism and Taoism.

Usui also is also said to have practiced Shugenja, also known as Shugendō, in addition to his practice as a Tendai Buddhist. Shugendō is a Japanese mountain ascetic shamanism, which incorporates Shinto and Buddhist practices. Roles of Shugendō practitioners include offering religious services such as fortune telling, divination, channelling, prayer, ritual incantations and exorcism. Shugenja was often used by family clans to heal disease or to avoid misfortune.