Kobo Daishi (774-835) is a Buddhist Monk. His original name is Kukai and the name Kobo Daishi was given to him posthumously. Monk Kukai is the founder of Shingon Sect (Shingan-Shu) of Buddhism and responsible building the sacred temple complex on Mt. Koya (Koyasan).
Many Buddhist temples in Japan are dedicated to Kobo Daishi, including large temples like Kawasaki Daishi Temple in the Kanto region.
At an early age, instead following prevailing Buddhist teachings such as Taoism (early Buddhist teachings in Japan in sixth century that came from China), Monk Kukai goes on a self awareness mission to China in 804. During this trip to China, he studies Zhenyang doctrine under the direction of the monk Huiguo and became a master of esoterism in 806.
After coming back to Japan, he started his own set of Buddhist teachings, which were later transformed into Shingon sect (Shingon-shu). The teachings of Monk Kukai preach that each person will be released from secular illusions and have his "mind's eye" opened. He then will be an awakened person to the actualities of life. He will then become a Buddha with his present body.
He was given the permission by then Emperor of Japan, (Emperor Saga) to build a temple complex on Mt. Koya (Koyasan) in the Wakayama prefecture and part of the Kii Peninsula. Under his leadership Koyasan has flourished as a grooming place for thousands of buddhist monks in the teachings of Shingon-shu.
Emperor Saga honored Monk Kukai with the directorship of Toji Temple in Kyoto city and gave it the official name Kyo-o-gokokuji, which means the temple that guards the capital (Kyoto city during the Heian period) and the land by virtue of Ninno-gokoku-kyo (the main teachings of the Shingon Buddhism). Kukai made Toji the central seminary of Esoteric Buddhism and added various other buildings to it.
Monk Kukai spent most of his later years in Mt. Koya (Koyasan) and he was later laid to rest in Koyasan. Monk Kukai's mausoleum is now a major destination for Buddhists and non Buddhists alike on Koyasan. Known as Oku-no-in, it is a must visit place for all followers of Buddhism.
Here is a video of Okunoin on Koyasan:
Monk Kukai, for his times, is considered as a renaissance man by Japanese people. He was known to have invented and developed the Hiragana (Japanese script language) and the first dictionary of Japanese words. He also devised the 88 temple pilgrimage of Shikoku (Shikoku Henro), which is considered as the fore father of all the temple pilgrimages in Japan.