Louis IX of France

Crowned at twelve in 1226 after his father's death, Louis spent his early years under his mother Blanche of Castile's regency as she crushed rebellious vassals and prosecuted the Albigensian Crusade. As an adult he fought England's Henry III to a standstill at Taillebourg, annexed provinces across Aquitaine and Provence, and overhauled French law - abolishing trial by ordeal, enshrining presumption of innocence, and creating a royal appeals system through new offices of provosts and bailiffs. His piety earned him the label "monk king," but it had teeth: he ordered Jews to wear yellow badges and burned the Talmud after the Disputation of Paris. A deathbed vow sent him on two disastrous crusades to North Africa and the Holy Land; captured and ransomed in the Seventh, he died of dysentery besieging Tunis in 1270 during the Eighth. His son Philip III inherited a kingdom at its medieval peak.