Won-Hyo was born in the town of Za-in-myon in Kyongsang Province in 617 AD. Legend has it that Won-Hyo's mother, while pregnant with him, was passing by a sala tree when she suddenly felt birth pangs, and, without having time to reach her home, gave birth to him there and then. The sala tree is significant, as it is usually only found in legends of highly revered figures.
The name given to him at birth was Sol Sedang. He derived the pen name Won-Hyo (meaning "dawn") from his nickname, "Sedak" (also meaning "dawn"). He assumed this pen name in later years, after he had become more accomplished as a Buddhist philosopher and poet.
Civil war amongst the Koguryo, Silla and Paekche kingdoms marked the period of Won Hyo's birth and childhood, and indeed it was not until 677 that the Silla dynasty unified Korea. Legend asserts that Won-Hyo, as a young man, took part in these bloody civil wars and saw many of his friends slaughtered, and it was this that drove him to turn his back on violence and become a monk. Most sources agree that he became a monk at the age of 20.
One story says he remodelled his home as a temple which he named Ch'ogae-sa; another says he simply shaved his head and went into the mountains to live as a monk. It is not even clear under which teachers he studied Buddhism; some say it was Nangji on Yong-ch'wi Mountain, others say he was a disciple of priest Popchang at Hungnyun-sa. Yet another legend has it that he learned the Nirvana Sutra from Podok, a Koguryo priest exiled in Silla. Buddhism was not a popular religion in Silla at that time, though; although it had been introduced into the kingdom of Koguryo in 372 and Paekche in 384, the general population of Silla was reluctant to accept it.
In 650, when Won-Hyo was 33 years old, he set out for China in the company of his friend Uisang; both of them had been inspired to study under the famous Buddhist scholar Huan-Tchuang. Their journey was smooth, except near the Chinese border in Liaotung, Koguryo, when they were mistaken for spies by sentries and barely escaped being captured. One of the most famous stories in Korean Buddhism concerns Won-Hyo's enlightenment during this attempted journey to China:
"One evening as Won-Hyo was crossing the desert, he stopped at a small patch of green where there were a few trees and some water. He went to sleep. Toward midnight he awoke, very thirsty. It was pitch-dark. He groped along on all fours, searching for water. At last his hand touched a cup on the ground. He picked it up and drank. Ah, how delicious! Then he bowed deeply, in gratitude to Buddha for the gift of water.
The next morning Won-Hyo woke up and saw beside him what he had taken for a cup. It was a shattered skull, blood-caked and with shreds of flesh still stuck to the cheek-bones. Strange insects crawled or floated on the surface of the filthy rainwater inside it. Won-Hyo looked at the skull and felt a great wave of nausea. He opened his mouth. As soon as the vomit poured out, his mind opened and he understood. Last night, since he hadn't seen and hadn't thought, the water was delicious. This morning, seeing and thinking had made him vomit. Ah, he said to himself, thinking makes good and bad, life and death. And without thinking, there is no universe, no Buddha, no Dharma. All is one, and this one is empty.
There was no need now to find a master. Won-Hyo already understood life and death. What more was there to learn? So he turned and started back across the desert to Korea."
His friend, Uisang, continued on to China and learned the doctrines of the Chinese school Hua-yen and later established this in Korea - as the Hwa-om school - when he returned.
Following his return, Won-Hyo undertook prodigious amounts of scholarly work, and his writing was not the only area in which he gained recognition. He was well-known both to the general population and to the members of the royal family and their court. He was often asked to conduct services, recite prayers, and give sermons at the royal court.
In 660 AD, King Muyo became so interested in Won-Hyo that he asked him to come and live in the royal palace of Yosok. A relationship with the royal princess Kwa developed, and marriage and the birth of their son Sol-Ch'ong soon followed. Shortly after his son was born, though, Won-Hyo left the palace to travel the country, and he became highly respected by the people of Korea. He hated the fact that different religions argued with each other over their different beliefs, so he created his own ideology in which the conflicts between various religions could be reconciled.
In 661 AD, he experienced a revelation in his Buddhist philosophy and developed the Chongto-Gyo ("pure land") sect. This sect did not require study of the Chinese Buddhist literature for salvation, requiring instead merely diligent prayer. This fundamental change in Buddhist philosophy made religion accessible to the lower classes, and as such it quickly became very popular among the entire population.
In 662 AD, Won-Hyo left the priesthood and devoted the rest of his life to travelling the country teaching his new sect to the common people. Won-Hyo's contributions to the culture and national awareness of Silla were instrumental in the unification of the three kingdoms of Korea.
Won-Hyo died in the year 686 aged 70, nine years after the unification of the Korean peninsula under the Silla dynasty. His body was laid in state by his son, Sol-Ch'ong, at Punhwang-sa temple.
It is said that during his lifetime Won-Hyo authored some 240 works on Buddhism; of these, 20 works in 25 volumes still exist. One of the forms he chose to use was a special Silla poetic form, Hyang-Ga. These poems were mainly written by monks or members of the Hwa-Rang and concerned patriotism, Buddhism, and praise of the illustrious dead. Won-Hyo's poem "Hwaorm-Ga" is said to be among the most admired of these poems.
During his lifetime Won-Hyo dominated the intellectual and religious arenas both inside and outside Korea, and made extensive commentaries on all the different schools of Buddhism that were competing for supremacy at that time. He set the shape and form of Silla Buddhism and was also the dominant figure in the Korean Buddhist tradition. Along with two other famous Korean Buddhists, Chinul and Sosan Taesa, Won-Hyo was one of the most influential thinkers Korea has ever produced.