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His sculling technique was so effective he won despite being, in rowing terms, a midget - just 5ft 9in (175cm) tall and weighing in at about 10 stone (64kg).
Born in Toronto in 1855, Hanlan grew up rowing around Toronto Bay, starting in a boat he built himself. At age 18 he was area champion, and in 1876 he won the enormously prestigious Philadelphia Centennial Exhibition regatta, effectively becoming champion of the USA. He rowed like "a small steam engine hissing through the water," according to the Toronto Globe.
In 1879 he came to England, beating champion sculler William Elliott on the Tyne before a crowd said to be ten thousand strong and betting heavily. The following year he beat the world champion, Australian Edward Trickett, on the Boat Race course on the Thames. Trickett was 6ft 4in (192cm) and 13 stone (82kg).
When Hanlan started his career, the sliding seat was very new. Scullers still pulled mainly with their arms. According to the Canadian Dictionary of National Biography: "Hanlan’s genius was a superbly efficient stroke – he was the father of the modern technique. He took full advantage of the sliding seat, not only to obtain greater reach but to drive with the large muscles of the legs in a coordinated, fluid motion so that the power of his whole body was marshalled into every stroke."
The powerful new technique gave Hanlan such a huge advantage he could indulge in stunts to humiliate opponents he disliked. In his race against Trickett, who he regarded as arrogant, he chatted to spectators, blew them kisses and rowed in zigzags before ostentatiously stopping and waiting for Trickett to catch up. He even pretended to collapse. According to historian Richard MacFarlane: "He had slumped forward, his oars drifting his boat slowing down under the burden of his weight and drag of the oars. Trickett turned to see his competitor and, filled with new hope, began to pull harder.... As Trickett pulled even with Hanlan, he cast a glance over to the motionless challenger. At that moment, Hanlan raised his head and flashed a smile at the champion. Trickett was shattered. Hanlan gave a wave to the crowd and pulled away once more...."
He won by three lengths. The crowd, needless to say, adored it, and the David against Goliath nature of the contest ran well in the press too.
He was idolised back in Toronto, helped by the fact that almost everyone "from judges to peanut vendors", according to the Globe, had backed him by telegraph bet and had won big.
It could not last, of course. In 1884 he was beaten by Australian William Beech, a huge and muscular blacksmith who had also cracked the correct way to use a sliding seat.
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The headland where he started his rowing career is now called Hanlan's Point and he is commemorated by a statue by Emanuel Otto Hahn, showing him standing proud and muscly, wearing just a pair of briefs and holding his blades.
(Thanks to Joe DesLauriers for the headsup)