Robert Francis St Clair-Erskine, 4th Earl of Rosslyn, styled Lord Loughborough from 1851 until 1866, was a British Conservative politician. He served as Captain of the Gentlemen-at-Arms under Lord Salisbury between 1886 and 1890.

The Captain of the Honourable Corps of Gentlemen-at-Arms is a post in the Government of the United Kingdom that has been held by the Government Chief Whip in the House of Lords since 1945. Prior to 17 March 1834, the Gentlemen-at-Arms were known as the Honourable Band of Gentlemen Pensioners.