William Stephen Ian Whitelaw, 1st Viscount Whitelaw, was a British Conservative Party politician who served in a wide number of Cabinet positions, most notably as Home Secretary from 1979 to 1983 and as de facto Deputy Prime Minister of the United Kingdom from 1979 to 1988. He was Deputy Leader of the Conservative Party from 1975 to 1991.

The deputy prime minister of the United Kingdom is the second highest ranking minister of the Crown and a member of the British Cabinet. The title is not always in use and prime ministers have been known to appoint informal deputies without the title of deputy prime minister. The incumbent deputy prime minister is Oliver Dowden who also serves as Chancellor of the Duchy of Lancaster and Secretary of State in the Cabinet Office.