Nicolaas Pieter Johannes ("Niklaas" or "Siener") Janse van Rensburg (3 August 1864 – 11 March 1926) was a Boer from the South African Republic – also known as the Transvaal Republic – and later a citizen of South Africa who was considered by some to be a prophet of the Boers (a segment of the Afrikaners.
Consequently, his nickname became Siener (Afrikaans for "seer").
Van Rensburg's visions were typically wrapped in a patriotic, religious format, and have been interpreted by believers as predictions of future events.
During the Boer War he became a trusted companion, if not advisor to General de la Rey and President Steyn.
The extent of his influence with these figures is disputed, though the devoutly religious de la Rey seemed to have considered him a prophet of God.