World War I Jan Christoffel Greyling Kemp (10 June 1872 – 31 December 1946) was a South African Boer officer, rebel general, and politician.

In June 1900, while serving under General Christian Frederick Beyers in the northern Transvaal he was elected a commandant.

This plan was abandoned and he became one of De la Rey's ablest and most daring officers, showing his tactical acumen particularly in the actions at Vlakfontein (29–30 May 1901), Moedwil (30 September 1901) and Battle of Ysterspruit, near Klerksdorp in the Western Transvaal on 25 February 1902.

In the Battle of Tweebos on 7 March 1902, where his horse was shot under him, he played a prominent part in capturing Lord Methuen's column.

On 11 April 1902, at Roodewal, in one of the last important actions of the war, Kemp launched a recklessly brave attack in De la Rey's absence, on Major-General RG Kekewich's forces, once again using a mounted charge over open terrain, which had become his characteristic mode of attack.

A South African court found him guilty of treason and sentenced him to 7 years in prison.

He was determined, direct, forceful, impetuous in the field and in politics and, above all, a fervent believer in the republican form of government for South Africa.