A simple answer - AP McCoy.
Knighted in 2016, McCoy is generally accepted as the finest rider the sport has ever produced, as a result of producing a record 4,358 winners in his time. He was also Champion Jockey a record 20 consecutive times, every year in fact he was a professional rider.
The Northern Irishman recorded his first winner back in 1992 at age of 17, claiming his first Champion Jockey title three years later.
McCoy won almost every major race there is to win, with his most high-profile winners being in the Cheltenham Gold Cup, Champion Hurdle, Champion Chase, King George VI Chase, and the 2010 Grand National aboard Don't Push It.
He was named BBC Sports Personality of the Year in 2010, becoming the first jockey to win the award, and in December 2013 he was named RTE Sports Person of the Year.
A simple answer, but perhaps not a simple explanation.