The painful image is all too familiar to those who make their lives with horses – the empty stall, where until this week Uncle Mo resided at Ashford Stud, posted on social media by Coolmore’s Adrian Wallace. But Uncle Mo, euthanized Thursday at a relatively young 16 following a leg injury, leaves a void bigger than a stall. The beloved Thoroughbred, a champion runner and an even better sire, left a sizeable mark on the sport. Owner Mike Repole, who rose to prominence when Uncle Mo became his first Grade 1 winner, said the stallion underwent surgery Wednesday for an injury to his left front leg – the nature and cause of which were not disclosed. However, “the recovery process was too much for him to endure,” Repole wrote on social media. “Uncle Mo was so much more to me than a champion and iconic stallion – he was and always will be a part of my family,” Repole continued. “Uncle Mo is the patriarch of Repole Stable. There will never be another horse that makes me feel or will impact my life the way that Uncle Mo has.” Others who considered Uncle Mo family include Ashford groom Rene Macias. “Rene was Uncle Mo’s devoted groom for all these years,” Coolmore wrote on social media. “He often said that Mo was his son, and it was clear that he loved him like one.” Uncle Mo, by Indian Charlie, was a yearling purchase by Repole and was trained throughout his career by Todd Pletcher. The colt won all three starts as a juvenile in 2010, bursting onto the scene with a 14 1/4-length debut romp at Saratoga. He won the Grade 1 Champagne by 4 3/4 lengths and the Breeders’ Cup Juvenile by 4 1/4 lengths and was voted the Eclipse Award as champion 2-year-old male. Uncle Mo won the Timely Writer to start his 3-year-old season, but incurred his first loss when third in the Grade 1 Wood Memorial. He was subsequently treated for a gastrointestinal tract infection. Inconclusive symptoms forced him to be scratched from the 2011 Kentucky Derby the day before the race. “Will never forget running into Todd just before the Derby draw and him telling me Uncle Mo might be a scratch,” trainer Graham Motion, who won that Derby with Animal Kingdom, recalled on social media. “The rest is history, who knows how good a race horse he might have been. We all know what a brilliant sire he has been. A huge loss.” A side note to Uncle Mo’s legacy is his Derby withdrawal – one of a series of high-profile scratches in those years – helped the final push to implement an also-eligible list for the race in 2012. That June, connections reported Uncle Mo was diagnosed with cholangiohepatitis, an inflammation of the liver and bile passages. The colt recovered to make his first start in more than four months in the Grade 1 King’s Bishop, finishing second by a nose to Caleb’s Posse, who went on to win the Breeders’ Cup Dirt Mile. Uncle Mo returned to the winner’s circle with a three-length score over older foes in the Grade 2 Kelso. In what was scheduled to be his final race, he finished 10th in the Breeders’ Cup Classic and concluded his career with a record of 8-5-1-1 and earnings of $1,606,000. But in some ways, his story was just beginning – the same for Repole, who had been thrust into the national spotlight. “If there was no Uncle Mo, then there would be no Repole Stable,” wrote bloodstock professional Jacob West, who has long been associated with the stable. “He was all class and good to so many people. Those of us associated with Repole Stable have been able to ride the wave that he started and has made it into what it is today.” Uncle Mo got off to a flying start as the leading freshman sire of 2015, establishing then-record earnings in the category. His son Nyquist followed in his footsteps with an unbeaten Eclipse championship campaign that year, capped by the Breeders’ Cup Juvenile. Nyquist went on to win the 2016 Kentucky Derby, became the leading freshman sire of 2020, and is now well-established as a successful stallion. Uncle Mo has ranked among the nation’s top 10 living general sires each year since 2019, and he was eighth on the 2024 list through Thursday. To date, he is the sire of 114 stakes winners, and versatility has been his hallmark. He is the sire of Belmont Stakes winner Mo Donegal – owned in part by Repole, giving him a cherished win in his home city. But Uncle Mo was represented at the same time by crack turf sprinter Golden Pal, a two-time Breeders’ Cup winner. He also sired Grade 1 winners A Mo Reay, Adare Manor, Arabian Knight, Bast, Dream Tree, Gomo, Kingsbarns, Mo Forza, Mo Town, Outwork, Unbridled Mo, and Yaupon. “When you think about the number of Thoroughbreds in the history of our sport that exemplified greatness at every stage of their career – from the racetrack to the breeding shed – the list is short,” stated Spendthrift Farm, which campaigned Kingsbarns and stands he, Mo Donegal, and Yaupon. “They are the true unicorns, and Uncle Mo was one of them.” Uncle Mo – also the broodmare sire of Grade 1 winners including championship candidate Thorpedo Anna – has several promising crops remaining in the pipeline. His current 2-year-olds include Grade 2 winners First Resort and Showcase. His yearlings were led by a $1 million colt at Keeneland September. The stallion, who was to stand for $125,000 in 2025, covered books of 243 and 202 mares in what proved his final two seasons, according to The Jockey Club’s Report of Mares Bred. :: Want to learn more about handicapping and wagering? Check out DRF's Handicapping 101 and Wagering 101 pages.