It was called the Chaplin before Hitler grew one. Hitler grew it to help soften his public image. He was known to be a big fan of American movies. And had them imported during WWII for private screenings, even though it was illegal in the rest of Nazi Germany.

I have always read that the style was in vogue among men who had to fight in WWI where the use of gas masks discouraged keeping a full beard or moustache as it hindered adherence.

You can see the shift in the American presidents too.