During Jack’s initial appearances in Doctor Who, Russell T Davies held a “half-hearted” theory that Jack would dress specific to the time period he was in, to contrast the Doctor who dresses the same wherever and whenever he goes. He is introduced wearing a greatcoat in World War II-set episodes, but changes to modern day jeans in contemporary episode “Boom Town” and black leather in futuristic episodes. Davies admits that this was a “bit of a lame idea” and decided that Jack “never looked better than when he was in his World War II outfit”.[104]
He’s got a jacket from fighting in the Napoleonic Wars; he’s got a snakeskin sword from Korea that I think he had to kill someone for; his boots are from Italy circa 1640 and he’s got gun holsters from the American West.“
The Committee to Nuke Elysium 