Why was Winston Churchill's father Lord Randolph Churchill, while Winston was just Mr. Winston Churchill?

Summary: “Lord” was a courtesy title given to Randolph because his father was a Duke. Randolph himself wasn’t a Duke and had no titles of his own, and didn’t have any to give to Winston, so Winston was just called Winston.

The longer explanation is this:

So we have Lord Randy, first of all. Lord Randolph Churchill, born 1849, was a third son of a Duke, John Winston Spencer-Churchill, the 7th Duke of Marlborough. Randolph has two older siblings, both male, though for this explanation we only really care about his eldest sibling, George, born in 1844. I’ll call him Brother George, because we also have a Grandpa George: John’s father, the 6th Duke of Marlborough.

Grandpa George had three titles: Earl of Sunderland, Marquess of Blandford, and Duke of Marlborough. While Grandpa was alive, all three titles were all officially held by Grandpa, but the two next in line in the entail/succession got to use them to make themselves sound cool. Therefore, Grandpa went by Duke, but Dad John was allowed to go by Marquess (“Lord John Spencer Churchill, Marquess of Blandford”) and four-year-old Brother George could call himself Earl, specifically George Spencer-Churchill, Lord Sunderland.

Grandpa George died in 1857, making Dad John the Duke. The moment Grandpa kicked the bucket, everyone “under” him—Dad John & Brother George and any kids of Brother George—moved up a rung in the ladder. Dad John became the Duke (AND the Marquess AND the Earl) and Brother George got to call himself Marquess.

George’s siblings (of which there were 11, including Lord Randy) all had courtesy titles, too. Theirs just weren’t as fancy as his, because they didn’t stand to inherit anything. So while George could go around telling all his school buddies to call him Marquess of Blandford, his brothers and sisters had to make do with being called Lord Randolph Spencer-Churchill and Lady Cornelia Spencer-Churchill. These Lord and Lady titles were for life, so even when Brother George became the actual Duke and HIS kids got to be Lords and Ladies, Randolph and his siblings kept their titles. The boys could share their titles with their wives—Randy’s wife was “Lady Randolph Churchill,” even though her real name was Jennie—but the girls couldn’t share theirs with their husbands. If Lady Cornelia married a street urchin, he didn’t get to be Lord Oliver Twist. (Same thing with Queens: Philip is a consort, not a King. But wives of Kings are Queens.)

The children of all these Lord Randolphs and Lady Cornelias don’t have titles, though. Because technically, the “Lord” and “Lady” are borrowed from their dad. Unless Randolph was given his own title and became the 1st Earl/Baron of Something, and he could pass it to his son, the titles stopped with him. His children got the surname of Spencer-Churchill, which was nothing to sneeze at, and a bunch of money, but no title.

I used: http://www.regencyresearcher.com/pages/titles2.html, http://laura.chinet.com/html/titles05.html, Wikipedia for names and dates. Any other page directed towards authors of Regency/historical fiction is a great resource for stuff like this! (See also: Debrett’s, Burke’s Peerage.) I did a lot with Victorian literature in college which is why I know this...try to make it through Thackeray’s Vanity Fair as an American without having to research titles. You can’t.