Andrew Bonar Law (1858-1923) was the son of a Presbyterian minister in New Brunswick, Canada, who was lucky enough to be sent when 12 to live with wealthy Glasgow banking cousins. He enjoyed a successful business career in the family bank and as partner in an iron trader, before entering Parliament at 42 and gaining a steady reputation as a business-oriented junior minister. He was elected Conservative leader as a compromise in 1911 with the vigorous backing of the dodgy Press baron Max Aitken, the future Lord Beaverbrook (1879-1964).
As leader, Bonar Law got on poorly with Asquith, exacerbating the poisonous political atmosphere of 1911-14, before establishing a good relationship with Lloyd George in the two wartime Coalitions. Having been instrumental in elevating Lloyd George to power, he was then instrumental in ejecting him at the Carlton Club meeting of October 1922, after which, much to his own surprise, his new Conservative government of ‘second-class brains’1 won a substantial outright majority over all other parties.
Bonar Law, a man of limited education and intellect, was Prime Minister for only seven months and had little independent impact on policy either before or during that period. There is no good reason why he should rank above other short-termers like Wilmington and Devonshire.
[1] The famous description of it by F.E. Smith, Lord Birkenhead (1872-1930) to which Baldwin is said to have replied that this was better than a government of second-class characters.