Magnús Óláfsson (died 24 November 1265) was a King of Mann and the Isles. He was a son of Óláfr Guðrøðarson, King of the Isles, and a member of the Crovan dynasty. Magnús' realm encompassed Mann and parts of the Hebrides. Some leading members of Magnús' family—such as his father—styled themselves "King of the Isles"; other members—such as Magnús and his brothers—styled themselves "King of Mann and the Isles". Although kings in their own right, leading members of the Crovan dynasty paid tribute to the Kings of Norway and generally recognised a nominal Norwegian overlordship of Mann and the Hebrides. Magnus was forced to cede lordship of the Isle of Mann to King Alexander III and swear fealty to him in 1264 after the Battle of Largs between the Norwegians and Scots after which the Norwegians retreated to Orkney.

In 1237, Óláfr died and was succeeded by his elder son, Haraldr, who later drowned in 1248. The kingship was then taken up by his brother, Rǫgnvaldr Óláfsson. After a reign of only weeks, Rǫgnvaldr was slain and the kingship was taken up by Haraldr Guðrøðarson, a descendant of Óláfr's half-brother and deadly rival, Rǫgnvaldr Guðrøðarson, King of the Isles. After a short reign, this Haraldr was removed from power by his overlord, Hákon Hákonarson, King of Norway. In Haraldr's absence, Magnús and a relation of his, Eóghan Mac Dubhghaill, King in the Isles, unsuccessfully attempted to conquer Mann. A few years later, Magnús successfully made his return to the island and was proclaimed king.

In the 1240s, following attempts to purchase the Isles from Hákon, Alexander II of Scotland resorted to warfare to win the region. His death in 1249 brought an abrupt end to his westward invasion, and it was not until the 1260s that a Scottish king again attempted to impose his authority into the Isles. In 1261, Alexander II's son and successor, Alexander III, attempted to purchase the Isles without success, before Scottish forces raided into the Hebrides. Hákon's response to Scottish aggression was to organise a massive fleet to re-assert Norwegian authority. In the summer of 1263, the fleet sailed down through the Hebrides. Although his forces gained strength as they sailed southwards, the Norwegian king received only lukewarm support from many of his Norse-Gaelic vassals—in fact, Magnús was one of the few who came out whole-heartedly for Hákon. At one point during the campaign, Hákon sent Magnús and some other vassals raiding deep into Lennox. Meanwhile, the main Norwegian force was occupied with the Battle of Largs—a famous, but inconclusive series of skirmishes against the Scots. Following this action, Hákon's demoralised fleet returned home having accomplished little. Not long after Hákon's departure and death, Alexander launched a punitive expedition into the Hebrides, and threatened Mann with the same. Magnús' subsequent submission to the Scottish king, and the homage rendered for his lands, symbolises the failure of Hákon's campaign, and marks the complete collapse of Norwegian influence in the Isles.

Magnús, the last reigning king of his dynasty, died at Castle Rushen in 1265, and was buried at the Abbey of St Mary of Rushen. At the time of his death, he was married to Eóghan's daughter Máire. In the year after his death, the Hebrides and Mann were formally ceded by King of Norway to the King of Scots. Ten years after Magnús' death, Guðrøðr, a bastard son of his attempted to establish himself as king on Mann. Guðrøðr's revolt was quickly and brutally crushed by Scottish forces, and the island remained part of the Kingdom of Scotland. By the 1290s, the Hebridean portion of Magnús' former island-kingdom had been incorporated into a newly created Scottish sheriffdom.

Magnús was a member of the Crovan dynasty—a line of Norse-Gaelic sea-kings whose kingdom encompassed the Isle of Man (Mann) and the northern parts of the Hebrides, from the late eleventh century to the mid thirteenth century. Although the kingdom originally encompassed the entirety of the Hebrides, much of the Inner Hebrides was permanently lost in the mid twelfth century, but the dynasty retained control of the largest Hebridean islands of Lewis and Harris and Skye. Magnús was the son of Óláfr Guðrøðarson, King of the Isles (died 1237). Although Óláfr is known to have had two wives, and no contemporaneous source names the mother of his children, Magnús' mother may have been Óláfr's second wife—Cairistíona, daughter of Fearchar, Earl of Ross, (died c. 1251).

Óláfr was a younger son of Guðrøðr Óláfsson, King of Dublin and the Isles (died 1187). Before his death in 1187, Guðrøðr instructed that Óláfr should succeed to the kingship. However, Guðrøðr was instead succeeded by his elder son, Rǫgnvaldr (died 1229), who had popular support. Rǫgnvaldr and Óláfr, who are thought to have had different mothers, subsequently warred over the dynasty's kingdom in the early thirteenth century, until Rǫgnvaldr was slain battling Óláfr in 1229. Rǫgnvaldr's son, Guðrøðr (died 1231), who was also in conflict with Óláfr, took up his father's claim to the throne, and at his height co-ruled the kingdom with Óláfr in 1231. Guðrøðr was slain in 1231, and Óláfr ruled the entire kingdom without internal opposition until his own death in 1237. Óláfr was succeeded by his son, Haraldr, who later travelled to Norway and married a daughter of Hákon Hákonarson, King of Norway (died 1263), but lost his life at sea on his return voyage in 1248. In May 1249, Haraldr's brother, Rǫgnvaldr (died 1249), formally succeeded to the kingship of the Crovan dynasty's kingdom.

Rǫgnvaldr Óláfsson's reign was an extremely short one; only weeks after his accession, he was slain on Mann. His killer is identified by a contemporary source as a knight named Ívarr who may have been an ally of Rǫgnvaldr Óláfsson's second cousin once removed, Haraldr Guðrøðarson (fl. 1249), who seized the kingship immediately following the killing. Although at first Haraldr was recognised as a legitimate ruler of the kingdom by Henry III, King of England (died 1272), Haraldr was later regarded as a usurper by his Norwegian overlord, Hákon. In 1250, Hákon summoned Haraldr to Norway to answer for his seizure of the kingship, and Haraldr was kept from returning to the Isles.

Eóghan Mac Dubhghaill, Lord of Argyll (died c.1268×1275) was a prominent member of Clann Somhairle, the descendants of Somhairle mac Giolla Brighde, King of the Isles (died 1164). Through Somhairle's wife, Ragnhildr, daughter of Óláfr Guðrøðarson, King of the Isles (died 1153), several leading members of Clann Somhairle claimed kingship in the Hebrides. In 1248, Eóghan and his second cousin, Dubhghall mac Ruaidhrí (died 1268), travelled to Hákon in Norway and requested the title of king in the Hebrides. Hákon subsequently bestowed the title upon Eóghan, and the following year, upon learning of Haraldr Óláfsson's death, Hákon sent Eóghan westward to take control of the Isles (at least temporarily) on his behalf. Up until this point Eóghan had two overlords: the King of Norway, who claimed the Hebrides; and the King of Scots, who claimed Argyll and coveted the Hebrides. Unfortunately for Eóghan, soon after his return from Norway, Alexander II of Scotland (died 1249) led an expedition deep into Argyll and demanded that Eóghan renounce his allegiance to Hákon. Eóghan refused to do so and was subsequently driven from his Scottish lordship.