Henry III of England was born on October 1, 1207, and became king at just nine years old after the death of his father, King John. His reign lasted from 1216 to 1272, making him one of the longest-serving monarchs in English history. Henry's early years were marked by the influence of regents and the struggle to establish his authority. During his reign, Henry III focused on strengthening the monarchy and expanding the royal lands. He is known for his efforts to rebuild Westminster Abbey and for his involvement in the Barons' Wars, which were conflicts with rebellious nobles. His reign saw significant political changes and the development of the English Parliament.