Ruaraidh Erskine of Marr (15 January 1869 – 5 January 1960) (Scottish Gaelic: Ruaraidh Arascain is Mhàirr) was a Scottish nationalist political activist, writer and Scottish Gaelic language revival campaigner.

Ruaraidh Erskine was born The Honourable Stuart Richard Joseph Erskine at 1 Portland Place, Brighton, East Sussex, England . He was the third of the four children born to William Macnaghten Erskine, 5th Baron Erskine (1841–1913), an army officer, and his wife, Caroline Alice Martha Grimble. The family were descendants of the Erskine Earls of Buchan.

Erskine claimed that he learned to speak Scottish Gaelic from his childhood nanny, who came from Harris, and that this kindled the enthusiasm which was to be a main hallmark of his career. His imagination was fired early by the Irish nationalist movement and these combined influences, together with his family's Scottish roots, led to his development as a prominent Gaelic nationalist, whose compelling dream was of a self-governing Celtic Scotland. As essential steps towards the realization of this dream he was actively involved in the fostering of Gaelic consciousness and in the extension of Gaelic usage, especially in the written form. He hoped that a significant extension of Scottish Gaelic literature would contribute to the raising of literary standards, in a reaction against what he saw as the degrading influence of music-hall and ‘pop’ culture on Gaelic verse in the second half of the nineteenth century. He probably also viewed his activity as a response to the dominance of folklore in the Gaelic literary world.

In 1890, Erskine and Herbert Vivian co-founded The Whirlwind, a weekly newspaper. The paper was published for less than a year, but printed works by a number of notable artists, including Walter Sickert and James NcNeill Whistler. It advocated nationalism, peace, free trade and Irish Home Rule, and opposed female suffrage and socialism. It also espoused a Jacobite philosophy, and the restoration of the House of Stuart. Erskine, along with Vivian and Melville Henry Massue founded the Legitimist Jacobite League of Great Britain and Ireland in 1891, and he was president of the organisation in 1893, 1894 and 1897.

In 1891, he stood as a candidate for the Buteshire constituency as a "Scottish Tory Home Ruler", but by October of that year, he had withdrawn.

In 1901, Erskine began to edit a new bilingual newspaper, Am Bàrd, which ran until July of the following year. In 1904, he launched Guth na Blaidhna, a bilingual periodical which promoted Scottish Gaelic language revival, Catholicism and a twentieth-century Counter-Reformation. It was published for 21 years, finally going out of business in 1925. Between February 1908 and February 1909 he published the weekly Gaelic language newspaper Alba, which covered a range of political and cultural matters, including land, crofting, fishing, Scottish Gaelic-medium education, early Scottish history and Gaelic song.

In 1914, Erskine revived The Scottish Review, a title which had been edited by the 3rd Marquess of Bute between 1882 and 1900. The journal's political stance became leftist as well as nationalist. Contributors included the Aberdonian trade unionist William Diack, James Maxton of the Independent Labour Party (ILP), the author and poet Lewis Spence, and the Welsh Nationalist MP Edward Thomas John.

In 1892, aged 23, he became vice-president of the Scottish Home Rule Association, but he grew to oppose the notion of home rule for Scotland within the United Kingdom and went on to support Scottish independence.