Baldwin III of Jerusalem

Baldwin III was crowned king at thirteen in 1143 after his father Fulk's death, but his mother Melisende kept true control of Jerusalem. He tried to prove himself in battle before turning fifteen - put down a rebellion at Wadi Musa in 1144, then stumbled in the Hauran and watched the Second Crusade fail at Damascus in 1148. By April 1152 he'd had enough: he deposed Melisende in a quick military move and finally ruled alone. The next year he captured Ascalon, the port that had eluded his predecessors, and began coordinating the other crusader territories after Raymond of Poitiers fell and Raymond II of Tripoli was assassinated. A near-disaster against Nur ad-Din in 1157 pushed him toward Byzantium; he married Emperor Manuel's niece Theodora and forged an alliance that shaped the kingdom's last decades. He died of illness in February 1163 with no heirs, leaving the throne to his brother Amalric.