Gary Oldman had been asked to play Winston Churchill a couple of times before and finally, he agreed to do so for the 2017 movie Darkest Hour. The main concern was the Prime Minister's bigger frame, as the actor wasn't planning on gaining so much weight. But the problem was solved with a special fat suit.

Although Oldman ruled out gaining weight, he wasn't as opposed to depicting a not very healthy habit of Churchill's–smoking. He smoked at least 400 Romeo y Julieta Cubans, which were the Prime Minister's favorite, and he actually got nicotine poisoning. But the director of the film, Joe Wright, remarked, "It's Winston Churchill. You can't have Winston Churchill without a cigar."

The actor explained how he managed to smoke $20,000 worth of cigars: "You'd have a cigar that was three-quarters smoked and you'd light it up, and then over the course of a couple of takes, it would go down, and then the prop man would replenish me with a new cigar — we were doing that for 10 or 12 takes a scene."