Ralph ("Nick") Nicholas Köster (born 22 February 1989 in Robertson) is a South African rugby union player. He last played professionally for Bristol in the position of Flanker or Eight Man. He is currently captain of Cambridge University R.U.F.C. Köster attended Bishops College in Cape Town and played in their First XV rugby team in 2006 and 2007. In 2006, he played alongside Martin Muller and Mathew Turner. Köster made the Western Province Craven Week side in 2006 and 2007 when he was captain. He was called up for South Africa Schools in both 2006 and 2007.