"hard, round, low-crowned hat," 1861, said to be from a J. Bowler, 19c. London hat manufacturer. A John Bowler of Surrey, hat manufacturer, was active from the 1820s to the 1840s, and a William Bowler, hat-manufacturer, of Southwark Bridge Road, Surrey, sought a patent in 1854 for "improvements in hats and other coverings for the head." But perhaps the word is simply from bowl (n.); compare Old English heafodbolla "brainpan, skull." The earliest usages are with a lower-case b-.