Alexander was king of Scotland, regarded as one of the country's greatest rulers. His reign marked a period of peace and prosperity in Scotland.
Alexander became king at the age of seven after the death of his father, Alexander II. In 1251 he married Margaret, the eldest daughter of Henry III of England.
In 1262, Alexander laid claim to the Western Isles, at that time ruled by Norway, continuing a policy that Alexander's father had pursued. King Haakon of Norway rejected the claim, but in 1263 he was defeated by the Scottish at the Battle of Largs. In 1266, by the Treaty of Perth, Norway gave Scotland control over the Isle of Man and the Western Isles.
Queen Margaret died in 1275. The death of Alexander and Margaret's three children between 1281 and 1284 prompted Alexander to marry again in an attempt to produce an heir. Five months after his second marriage, on 19 March 1286, Alexander died after falling from his horse.