Archibald Sinclair, 1st Viscount Thurso

Archibald Henry Macdonald Sinclair, 1st Viscount Thurso KT, CMG, PC (22 October 1890 – 15 June 1970), known as Sir Archibald Sinclair, Bt between 1912 and 1952, and often as Archie Sinclair, was a British politician and leader of the Liberal Party.

Background and education
Sinclair was the son of a Scottish father and an American mother. He was the great-great-grandson of Sir John Sinclair, 1st Baronet. In 1912 he succeeded his grandfather Sir John Sinclair, 3rd Baronet as fourth Baronet, of Ulbster. Educated at Eton College and the Royal Military Academy Sandhurst, he was commissioned into the Life Guards in 1910.

Military career
Sinclair served on the Western Front during the First World War and rose to the rank of Major in the Guards Machine Gun Regiment. He served as second-in-command to Winston Churchill when Churchill commanded the 6th Battalion of the Royal Scots Fusiliers in the Ploegsteert Wood sector of the Western Front in 1916, after Churchill had resigned as First Lord of the Admiralty. They formed a lasting friendship that would become a significant political alliance in later decades. From 1919 to 1921 he served as Personal Military Secretary to Churchill when he returned to the Cabinet as Secretary of State for War, then accompanied him to the Colonial Office as Private Secretary.

Political career
In 1922 Sinclair entered the House of Commons as a Liberal Member of Parliament (MP) for Caithness and Sutherland, supporting David Lloyd George and defeating the incumbent Liberal supporter of H. H. Asquith. His constituency was the largest, in terms of area, in the United Kingdom. He rose through the Liberal ranks as the party shrank in Parliament, becoming Chief Whip by 1930. In 1931 the Liberal Party joined the National Government of Ramsay MacDonald, with Sinclair appointed Secretary of State for Scotland. He was sworn of the Privy Council at the same time. The following year he, together with other Liberal ministers, resigned from the government in protest at the Ottawa Conference introducing a series of tariff agreements. Sinclair and the Liberal leader, Sir Herbert Samuel, were thus the last Liberal politicians to sit in the Cabinet until 2010.

In the 1935 general election, Samuel lost his seat. Sinclair became the party's leader at the head of only twenty MPs. With the party now clearly marginalised as the third party on the fringe, with few distinct domestic policies, with a parliamentary party that was primarily a collection of individuals elected as much for themselves as for their party, and with the separate Liberal Nationals offering competition amongst Liberal-inclined voters, Sinclair fought to make the Liberals once more a relevant force in British politics, taking up the issues of opposition to the continental dictatorships and working closely with Winston Churchill who was a backbencher at that time and generally shunned by his Conservative Party. When Churchill formed an all-party coalition government in 1940, Sinclair became Secretary of State for Air. However he did not sit in the small War Cabinet, though he was invited to attend meetings discussing any political matter. As Secretary for Air, he played a leading role in planning the fire-bombing and destruction of Dresden. He remained a minister until May 1945 when the coalition ended. In the 1945 general election, he narrowly lost his seat. His margin of defeat is one of the tightest on record - he came third, even though the victor had only 61 votes more than he.

There was speculation that he might return to the Commons and the leadership, as the Conservative victor in his seat had promised to only serve in parliament until the end of war with Japan, a pledge he kept modifying to serving just one more year, every year. Sinclair awaited the imminent by-election, which never materialised. At the 1950 general election Sinclair again stood for his old seat and moved to second place, but in yet another close election, he remained 269 votes away from victory. In 1952, the year of his first stroke, he accepted elevation to the House of Lords as Viscount Thurso, of Ulbster in the County of Caithness. He was expected to take up the leadership of the Liberal group in the House of Lords, but a much more serious stroke in 1959 left him largely bedridden and in a state of precarious health until his death in 1970.

Family
Sinclair married Marigold (1897-1975), daughter of Lieutenant-Colonel James Stewart Forbes, in 1918. They had four children: the Hon. Catherine (1919-2007), the Hon. Elizabeth (1921-1994), Robin (1922–1995), and the Hon. Angus (born 1925). Sinclair was one of the largest landowners in the United Kingdom, owning an estate of about 100,000 acres (400 km²) in Caithness. He was handsome and charming and regarded as a daredevil, but in private life was rather shy, reserved and antisocial, with a slight speech impediment.

In the 1990s, his grandson, John Thurso, entered politics and has sat since 2001 as the Liberal Democrat MP for his grandfather's seat, now called Caithness, Sutherland and Easter Ross. Sinclair's granddaughter, Veronica Linklater, Baroness Linklater of Butterstone (daughter of the Hon. Elizabeth Sinclair), is also a Liberal Democrat politician.