This song refers to Bobs, who was Frederick Sleigh Roberts, later known as Earl Roberts of Kandahar, Pretroria and Waterford.
As the second British commander in chief in the South African war (December 1899-November 1900) he ended a succession of British defeats; captured Bloemfontein, took the cities of Johannesburg and Pretoria and defeated the Boers at Bergendal.
Earl Roberts earned the name from a poem Rudyard Kipling wrote about him entitled Bobs which can be found in Barrack room ballads published in 1892.