Alexander III (Medieval Alaxandair mac Alaxandair; Modern Gaelic: Alasdair mac Alasdair; 4 September 1241 – 19 March 1286) was King of Scots from 1249 until his death. He concluded the Treaty of Perth, by which Scotland acquired sovereignty over the Western Isles and the Isle of Man. His heir, Margaret, Maid of Norway, died before she could be crowned.
Alexander was born at Roxburgh, the only son of Alexander II by his second wife Marie de Coucy. Alexander's father died on 6 July 1249 and he became king at the age of seven, inaugurated at Scone on 13 July 1249.
The years of his minority featured an embittered struggle for the control of affairs between two rival parties, the one led by Walter Comyn, Earl of Menteith, the other by Alan Durward, Justiciar of Scotia. The former dominated the early years of Alexander's reign. At the marriage of Alexander to Margaret of England in 1251, Henry III of England seized the opportunity to demand homage from his son-in-law for the Scottish kingdom, but Alexander did not comply. In 1255, an interview between the English and Scottish kings at Kelso led to Menteith and his party losing to Durward's party. But though disgraced, they still retained great influence, and two years later, seizing the person of the king, they compelled their rivals to consent to the erection of a regency representative of both parties.
On attaining his majority at the age of 21 in 1262, Alexander declared his intention of resuming the projects on the Western Isles which the death of his father thirteen years before had cut short. He laid a formal claim before King Haakon IV of Norway. Haakon rejected the claim, and in the following year responded with a formidable invasion. Sailing around the west coast of Scotland he halted off the Isle of Arran, and negotiations commenced. Alexander artfully prolonged the talks until the autumn storms should begin. At length Haakon, weary of delay, attacked, only to encounter a terrific storm which greatly damaged his ships.