William Sinclair, 1st Earl of Caithness, last Earl (Jarl) of Orkney (1434–1470 de facto, –1472 de jure), 2nd Lord Sinclair and 11th Baron of Roslin was a Norwegian and Scottish nobleman and the builder of Rosslyn Chapel, in Midlothian.

Malcolm Ian Sinclair, 20th Earl of Caithness, (born 3 November 1948), is a Scottish Conservative politician and member of the House of Lords as one of the remaining hereditary peers.