Blanche of Castile was born in Palencia, Spain, on March 4, 1188, to Alfonso VIII, King of Castile, and Eleanor of England. Her maternal grandmother, Eleanor of Aquitaine, was the most powerful woman in Europe at the time. Eleanor, noticing Blanche's personality and temperament, endeavored to secure Blanche a match to the French dauphin. In 1200, Blanche's uncle, King John of England, managed to sign a treaty with France prompting the union; Blanche was married to Louis shortly thereafter.
King John died in 1216 and Blanche decided she would seize the throne of England. Louis supported his wife and invaded England in her name. England, however, was ready for him and rebuffed the French advances. The attempt was a miserable failure.
Roughly ten years after the debacle in England, Blanche became a staunch enemy of the Cathar movement, which was a sect that believed good and evil had separate creators. Her animosity against the Cathars was possibly what drove Louis to make war on them. On his way home after that campaign, he was stricken with dysentery and died as a result.
In his death, Louis left his preteen son, also named Louis, on the throne as king. Blanche was regent during her son's minority. Shortly into the regency, she was confronted by nobles, who were supported by Henry III of England and the illegitimate son of King Philip II Augustus, Philip Hurepel, whose goal was to depose her and young Louis. Blanche, however, was a great tactician and scrupulously ousted any barons who weren't completely loyal to herself or her son, and successfully quashed any and all attempts by them to achieve their ends.
In 1229, there was an altercation between Parisian university students and an innkeeper that resulted in the police beating the students relentlessly and dumping their bodies into the Seine. Blanche, who had been given bad advice, sided with the police. This prompted the university to go on strike and most of the students left. It would be many years before Blanche would successfully negotiate the university's return.
Louis suffered from an illness in 1144, after he'd reached his majority. When he recovered, he and his wife decided they would start a new Crusade in the Holy Land. Blanche was adamantly against this, but there was little she could do to stop him. He was, after all, king; thus Blanche was left once more to act as regent for her son. Louis was captured at some point during the Crusade and Blanche, as a mother and regent, appealed to her own parents and everyone else with political power and sway to secure his release.
It was during Blanche's second term of regency that she suffered a heart attack as she was heading to aid the poor in Paris. She was returned to the Louvre, where she died after asking for forgiveness of her sins. Louis, who would go on to be canonized as a saint, was still in the Holy Land when he heard of his mother's death.