London: His moustache is the most instantly recognisable - and sinister - in history.
Yet, according to new research into Adolf Hitler's early life, the distinctive, toothbrush shape that adorned his scowling face was not his first preference.
A previously unpublished essay by a writer who served alongside Hitler in the First World War trenches reveals the future Fuhrer was only obeying orders when he shaped his moustache into its tightly-clipped style.
He was instructed to do so in order that it would fit under the respirator masks, introduced in response to British mustard gas attacks.
Had that order never been issued, the tyrant who brought most of Europe to its knees would be remembered as a man with a large Prussian moustache.
The prosaic explanation comes in a new biography of the writer Alexander Moritz Frey, who came to know him when both were lowly privates in a Bavarian infantry division.
In a hitherto unpublished essay, Frey, who died in 1957, wrote of his first meeting with Hitler in 1915: "A pale, tall man tumbled down into the cellar after the first shells of the daily evening attacks had begun to fall, fear and rage glowing in his eyes.
"At that time he looked tall because he was so thin. A full moustache, which had to be trimmed later because of the new gas masks, covered the ugly slit of his mouth."