King John
King John (1199-1216) was an Angevin monarch of England, who attained the English throne following the death of his brother, King Richard I in 1199. His rule has been characterised as one of mediocrity, but historians have recently begun to claim that John was a better king than the scribes have accounted for. He was succeeded by his young son Henry, who became Henry III on his coronation.
Magna Carta
John's rule met with resentment from the aristocrats, who came together to force him to sign Magna Carta, a charter that would limit royal power and guaranteed civil liberties, such as the habeas corpus for the nobles. The document later became the basis of constitutional monarchy in Britain, the foundation for the modern legal code, as well as being a precursor of the Napoleonic Code.