The claim that the 'Gregor' who was the Clan namefather was either the son or the brother of Kenneth MacAlpin, the first paramount King of Scotland, is unproven. He was probably the second Chief of the clan, succeeding his father, 'One-eyed' Iain as late as 1390.

The homelands of the MacGregors were the three glens of the rivers Strae, Orchy, and Lochy, now the heartland of the Campbells.

It was the expansion of the powerful Campbells which led to the MacGregors becoming landless outlaws. The most unscrupulous branch of the Campbells , by 1519 calling themselves by the old MacGregor title 'of Glenorchy', appointed as Chief of Clan MacGregor a younger chieftain who had been forced to marry a Campbell heiress whom he had ravished.

The true heirs to the leadership of the Grigorach were driven to continuing their struggle as guerillas in the mountains of Argyll and Perthshire, earning the nickname 'Children of the Mist'. Their Chief was captured in 1552 and personally beheaded by Black Duncan Campbell of Glanorchy, the brother of the ravished heiress.

Fifty years later, the MacGregor's policy of taking bloody revenge for each instance of persecution led to a 400-strong force of Colquhouns (Campbell allies) being sent, on the orders of King James VI, to wipe out 'the haill tribe, root and branch'. The MacGregors and their allies ambushed the advancing Colquhouns in Glen Fruin, slaughtering over a hundred of them.

The King issued a special order outlawing the Clan MacGregor and forbidding anyone, on pain of death, to bear the MacGregor name. The Chief, Alexander MacGregor of Glenstrae, was hanged with many of his followers in Edinburgh. The Clan were thus proscribed and persecuted until 1774, when the Act against the clan, its people, and their name was repealed. As a result, many people today, who are of the MacGregor clan use the names adopted during the two centuries when the clan name was forbidden.