William David Trimble, Baron Trimble, PC (born 15 October 1944, in Belfast), is a politician from Northern Ireland. He served as Leader of the Ulster Unionist Party (UUP; 1995–2005), was the first First Minister of Northern Ireland (1998–2002), and was a Member of the British Parliament (1990–2005). He is currently a life peer for the Conservative Party. Trimble was awarded the 1998 Nobel Peace Prize, along with John Hume.

While a professor of law at Queens University, he was elected to the Northern Ireland Constitutional Convention. He served as Member of Parliament for Upper Bann from 1990 until 2005. He resigned leadership of the UUP soon afterwards. In June 2006, he became a member of the House of Lords, as The Right Honourable William David Trimble by the name, style, and title of Baron Trimble, of Lisnagarvey in the County of Antrim. In April 2007 he left the UUP to join the Conservative Party.

In June 2010, the Israeli government appointed Lord Trimble to be one of two international observers serving on an Israeli commission of inquiry looking into the events surrounding an Israeli raid on the Mavi Marmara, along with Canadian former Judge Advocate General Ken Watkin.