William David Trimble, Baron Trimble, PC (born 15 October 1944), is a politician from Northern Ireland who served as leader of the Ulster Unionist Party (UUP) and was the first First Minister of Northern Ireland. He is currently a life peer for the Conservative Party.

He shared the 1998 Nobel Peace Prize with John Hume of the Social Democratic and Labour Party. He served as Member of Parliament for Upper Bann from 1990 until 2005, when he was defeated in the British general election and resigned the 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 announced that he was to leave the UUP and join the Conservative Party.

David Trimble was educated at Bangor Grammar School in Bangor, County Down, and at the Queen's University of Belfast (QUB), where he received a First class honours degree, becoming a Bachelor of Laws (LL.B). He qualified as a barrister in Northern Ireland in 1969 and became a lecturer in law at QUB, becoming a Senior Lecturer in 1977. He served as head of the Department of Commercial and Property Law from 1980 to 1989.