Stephen Dillane (born 27th March 1957) is a British actor experienced with roles on both stage and screen. He is arguably best known for his Emmy-nominated performance as Thomas Jefferson in the HBO mini-series John Adams. He has also appeared as Leonard Woolf in The Hours, Merlin in King Arthur and Horatio in the Mel Gibson-starring version of Hamlet. His son, actor Frank Dillane, portrayed the teenage Lord Voldemort in the film adaptation of Harry Potter and the Half-Blood Prince.