Henry III, KingHenry III, King /ˌhenri ðə ˈθɜːd $ -ˈθɜːrd/(1207–72) the king of England from 1216 until his death. He fought many wars in Europe, and this made him unpopular with the barons (=men of the highest social class). Led by Simon de Montfort, they fought against him but eventually lost.