Historical figure · People
Beau Brummell
The man who replaced ornament with fit, and made restraint the most conspicuous thing a man could wear.
George Bryan 'Beau' Brummell dominated English men's dress in the first decades of the nineteenth century. His contribution was subtraction: dark, plain coats, immaculate linen, precisely cut trousers, and an insistence that a garment's quality lay in its fit and its cleanliness rather than its decoration. Nearly everything about modern men's clothing follows from it.
What he actually changed
Before Brummell, elite male dress meant colour, embroidery, silk, and visible expense. After him it meant dark cloth, white linen, and a coat cut so precisely that the cut itself was the display. He is reported to have spent hours dressing and to have insisted on garments being remade until they were right. The consequence was to move the whole basis of male elegance from ornament to tailoring, which is why the modern trade exists in the form it does. A cutter's skill became the thing being bought.
The hygiene point
Brummell's insistence on daily bathing and fresh linen was genuinely unusual and is a real part of the contribution: clean, well-fitted, unadorned clothing as a standard rather than an eccentricity.
He died in poverty in Caen in 1840, having quarrelled with the Prince Regent and fled his creditors. The aesthetic outlived him completely.
How the influence travelled
Brummell had no title, no fortune of consequence and no office. His authority was social, exercised through the Prince Regent's circle, and it spread because the people around him copied him and were themselves copied. Within twenty years the dark, plain, precisely cut coat was standard across Europe. That is worth noticing as a mechanism. Menswear has almost never changed by decree; it changes when a small number of conspicuous people do something and everyone else works out why.