Hojo Masako was born in 1157, the first daughter of Hojo Tokimasa. The Hojo family were self-proclaimed descendants of the Taira clan. Much of Masako's childhood was filled with happiness, due to her two younger brothers, Yoshitoki and Tokifusa. Masako also had another brother, Yasutoki, who was born in 1183.
Masako was born during a time of many political conflicts. In 1156, the Hogen Insurrection had succeeded in establishing supremacy of the bushi over the court nobility. Then in 1159, a struggle between the Minamoto Clan and the Taira Clan, called the Heiji Insurrection broke out. In the conflict that ensued, Minamoto Yoshitomo, a prominent Minamoto general, was executed. Yoritomo, Yoshitomo's son, was spared from death, but was banished to Izu Hirugashima, an island off the coast of Izu.
In 1177, when Masako was 21, she married Yoritomo, who was 31. Their marriage was unique for the time period, in that it was one based on love, rather than one based on political maneuvers, and was looked down upon by Masako's father, Tokimasa. He objected largely because he was now father-in-law to his family's archenemy. To remedy this problem, Tokimasa promised his daughter to Yamamoto Kanetaka.
However, Masako was not able to forget about her love, and rejected her new husband. Then, being able to take no more, she escaped from her "prison" in Izu during a storm. Masako then cautiously followed a mountain path to Izuyama Gongen, the new hideout of Yoritomo. Masako gave birth to her first son in 1182, Minamoto Yoriie.
In 1199, Yoritomo passed away, and Masako decided to live the life of a nun. Despite these decisions, Masako aided her father in securing the power of the Hojo family in Kamakura. One of Masako's first political actions was to organize a council that was to protect her son, Yoriie.
Then, around 1203, Yoriie had allied with the Hiki family to kill Hojo Tokimasa, and overthrow the ruling power of Kamakura. However, Masako overheard these plans and reported them to her father. Tokimasa quickly took action, and killed the leaders of the Hiki family, and sent Yoriie to Izu in exile, where he was later murdered.
Later, in 1218, Masako's brother, Yoshitoki, took over as the head of the Hojo, and showed support for the shogun Minamoto Sanetomo. That year, Masako, still serving her family, went to Kyoto, to meet with the retired emperor Go-Toba, and suggest that he allow Sanetomo, who was without an heir, to adopt one of his sons. The attempt was, in the end, pointless, for in 1219, Sanetomo was murdered.
Finally, Masako's youngest brother, Yasutoki, assumed the regency. Shortly after that, Masako died at the age of 69, in 1225. Hojo Masako is also remembered as encouraging Gokenin to fight during the Shokyo disturbance (thanks Shro0m), and was then given the nickname "Amashogun", or "nun-shogun".