John W. Sadler (born July 30, 1956 in Long Beach, California) is an American horse trainer in the sport of Thoroughbred horse racing.

A former show jumper rider, who tried out for the U.S. Olympic Equestrian team and walked hots for trainer Tom Pratt at Santa Anita Park during his high school years. Sadler later attended the University of Oregon and once his studies were complete, he returned to Southern California to work alongside the late Dr. Jack Robbins as his veterinary assistant. Later he would act as David Hoffmans assistant trainer and began his own career when he acquired a string of Eddie Gregson’s horses and traveled north to Golden Gate Fields in the late 70’s. Sadler took out his trainer’s license in 1978 at the age of 22 and won his first race in 1979.

In 1991 John Sadler won the first match race in the history of Santa Anita Park when Valiant Pete, winner of the 1990 California Cup Sprint, equaled the world record of 0:44 2/5 for four furlongs in defeating champion American Quarter Horse Griswold in a $100,000 winner-take-all race.

At Hollywood Park on June 28, 2008, Sadler won three stakes races when Whatsthescript won the Grade II American Handicap, Dearest Trickski triumphed in the Grade II A Gleam Handicap, and Emmy Darling won the Landaluce Stakes. On December 26, 2010, he repeated this performance at Santa Anita, as Twirling Candy won the Grade I Malibu Stakes, Switch won the Grade I La Brea Stakes and Sidney's Candy won the Grade II Sir Beaufort Stakes. Sadler won 3 stakes races for the third time at Hollywood Park on July 17, 2012 when Scherer Magic won the Grade III Hollywood Juvenile Championship, Switch in the Grade II A Gleam Handicap, and Lady of Shamrock in the Grade I Hollywood Oaks.

Sadler’s stunning 2008 season landed him amongst the nation’s Top 10 trainers at the age of 52. His purse earnings stood at $6.6million with two months still to go in the year. He had saddled 20 stakes winners and captured back-to-back training titles at both Hollywood Park’s spring/summer meet and at Del Mar after having achieved his first-ever career championship at Hollywood Park’s Autumn Meet the previous year. He closed out 2008 with earnings of over $7.3 million in earnings

Following a seventh place finish nationally in 2010 with earnings of just over $7.3 million, Sadler was on target for another Top 10 finish in 2011 following a terrific start during the Santa Anita Winter meet, which included victories in four Grade I events.

Carving out two of his best year’s yet, Sadler saddled three Grade I winner’s in 2015 and oversaw the Eclipse Award Champion campaign of his prized his 3-year-old filly, Stellar Wind. 2016 and 2017 showed no signs of slowing down as Stellar Wind won multiple Grade I events, retiring at the end of 2017. Coolmore bought her for $6 million, the co-second-highest-price ever paid for a broodmare prospect at Keeneland. 

2017 also brought a brilliant Grade 1 win for the Sadler trained Lookin At Lucky colt, Accelerate.  He beat out Arrogate by 8 lengths to take home the win in the TVG Pacific Classic. 

2018 is starting off nicely with four grade stakes wins, including the $600,000  Grade 1 Santa Anita Big Cap and the Grade 2 Santa Monica Stakes.