The Keeper of the King's/Queen's Swans was a late medieval-founded office in the Royal Household of the Sovereign of England, later Great Britain and ultimately the United Kingdom. He was earlier called the King's/Queen's Swanmaster. The office existed to perform Swan-Upping marking and health-checking carried out using Thames skiffs on many of the non-tidal reaches of the River Thames in latter years from Sunbury-on-Thames passing Windsor, Berkshire to Henley on Thames. In 1993 it was replaced by two separate offices: Warden of the Swans and Marker of the Swans.