Ruth Mary Cavendish-Bentinck (née St Maur; 21 October 1867 – 28 January 1953) was a Morocco-born British aristocrat, suffragist and socialist.

Bentinck was born in Tangier in 1867, the illegitimate daughter of aristocrat Ferdinand Seymour, Earl St. Maur, and a housemaid, Rosina Elizabeth Swan.

[3] Her illegitimacy was a problem during her childhood but this was balanced by the education and care that her de facto parents gave her.

[5] In 1912, Bentinck and Florence Gertrude de Fonblanque organised a suffrage demonstration that involved women dressed in brown, green and white walking from Edinburgh to London.

[3][6] His older brother was William George Cavendish-Bentinck, British Member of Parliament who married the American heiress, Elizabeth Livingston (who had two girls but no boys).

[7] Together, Ruth and Frederick were the parents of four surviving children, including:[8] Bentinck died at her home on Marylebone Road in London in 1953.