For a legendary gambler who thinks nothing of betting a million dollars on one horse, Irish businessman JP McManus is by all accounts a surprisingly reserved man.

From humble beginnings as a bookmaker, McManus earned a reputation as the fearless man on the track who would take on any wager -- no matter how big.

"He's an absolute legend. He's got balls of steel when it comes to placing bets," says Barry Orr, spokesman for Betfair, the world's biggest online betting exchange.

Now worth an estimated $1 billion, the 62-year-old property mogul and horse owner was a big player at this week's Cheltenham Festival -- one of the biggest betting events in the Britain.

Described as the "Olympics of jumps racing," more than $820 million is bet during the four-day festival, with many punters taking their lead from the almost-mythical McManus.

"McManus is a legendary figure because of how brave he is," Ladbrokes bookmaker David Williams says. "He's one of those faces that when he walks into a betting ring, everyone is wondering what he's going to do.

"But you'd never believe he's such a big, brazen better -- he's very polite, very unassuming, a real gentlemen."

Nicknamed the "Sundance Kid" for his bold gambling, McManus famously won $1.3 million in just one day at Cheltenham in 2006, in series of wagers with similarly daring bookmaker "Fearless" Freddie Williams.

As Cheltenham wraps up for another year on Friday, CNN's Winning Post takes a look at five of the most incredible horse racing betting stories of all time.

Stable boy-turned-millionaire

This time last year, 29-year-old Conor Murphy was a stable boy -- until one lucky bet at Cheltenham changed his life forever.

The Irishman could have been accused of letting his heart rule his head when he bet $75 on all five of his boss's horses winning.

But Murphy happily proved the skeptics wrong, scooping $1.5 million in an accumulator -- a single bet which relies on all horses winning.

Murphy placed the wager online three months before the race, giving him greater odds -- and greater returns -- than those betting on the day.

The huge windfall helped finance his lifelong ambition of working as a trainer in Louisville, home of the prestigious Kentucky Derby, he told British newspaper The Telegraph.

Against the odds

If ever there was an opportunity to step back in time and place a bet, it would surely be on the Kentucky Derby's 1913 winner Donerail.

The three-year-old colt remains the highest odds winner in the history of the race, placed at 91-1, said the Kentucky Derby Museum.

One hundred years ago, those putting $2 on Donerail would have collected $184.90 in winnings. By today's standards, it's roughly the equivalent of placing a $46 bet and getting $4,300 back.

Surprise winner Donerail pulled away at the last stretch, setting a new track record with a time of two minutes and four seconds, beating his nearest rival by half-a-length.