Background
He was a son of David Ker, Member of Parliament for Athlone 1820-1826 and Downpatrick 1835-1841, and Selina Sarah, daughter of the first Marquess of Londonderry, and the younger brother of David Stewart Ker, the Member of Parliament for Downpatrick, 1841-1847 and 1859-1867 and one of the Members of Parliament for County Down, 1852-1857.