ARCADIA, Calif. Mark Glatt stood in the grandstands at Santa Anita Park last week and watched a 3-year-old bay colt on the other side of the racetrack.Then the horse took off.A veteran trainer, Glatt studied the horse as it ran in the cool morning air with a rider aboard, down the backstretch, through the far turn, down the homestretch and across the finish line.He went 5/8ths in 59 and 3, Glatt later told USA TODAY Sports, meaning the horse covered 5/8 mile in 59.6 seconds. I thought the work was excellent. He seemed very happy.Well, of course he did.The horse named So Happy, who sold for a modest $20,000 at a yearling sale, is headed for the Kentucky Derby. He is listed at 15-1 by TwinSpires.com for the race May 2 at Churchill Downs in Louisville, and So Happy also stands at the center of a heartbreaking and heartwarming story.Among those cheering are a 28-year-old horseman from Venezuela, a 60-year-old jockey and a 94-year-old breeder.Then theres Glatt, the 53-year-old trainer who has the first Kentucky Derby horse. It became official when So Happy won the Santa Anita Derby April 4, less than eight weeks after Glatts wife, Dena, died of heart failure.Glatt now wears a bracelet with some of his wifes ashes inside of it.That way I always have her with me, he said.'We were optimistic'Glatt, whosehorse-training operationis based in Southern California, is known as skillful and stoic, even grumpy. When he bought a bay colt at a sale of 2-Year-Olds in 2025, his clients Hans and Ana Maron of Arizona wanted the horse.Custom called for the Marons to pick a name.And I see the dad is Runhappy, the mothers So Cunning, Ana Macron said. And I remember saying, 'Mark, I found the perfect name and I'm going to name it after you because you're always so happy.'We all laughed. Dena (Mark Glatts wife) couldn't get enough of it. She kept laughing. And it's sad because of what happened.As So Happy emerged as a special horse. Dena Glatt unexpectedly developed heart problems.We actually watched the Super Bowl with her at the hospital, Ana Maron said. We went home and we were optimistic. And then two days later, she had a heart attack and passed away.Dena Glatt, who had raised three children with Mark Glatt, was 57.About the only one unaffected by the death was So Happy, who wears blinkers during training because he gets distracted.Just like a kid that likes to throw things up in the air and watch it blow away, Hans Maron said. He's kind of that big kid having fun.From humble originsThe most expensive racehorse ever was Fusaichi Pegasus, reportedly sold for $70 million in 2000.Then there are the likes of So Happy.So Happys mother is So Cunning, a broodmare owned by Leverett Miller, a 94-year-old horse breeder in Florida. He said it was the last horse he co-owned with his late wife, and it had bargain-basement roots. Miller said he paid $2,700 for So Cunnings great grandmother and that So Cunning also descended from a stallion whose stud fee was about $1,000.So Happys father is Runhappy, a champion sprinter who was retired in 2016 with an initial stud fee of $25,000. The fee dropped in half by 2022, with Runhappy having failed to produce many talented offspring. At the same time, Miller was looking for a horse to mate to So Cunning.He gambled on Runhappy.Born in 2023, So Happy went for $12,000 at a weanling sale. He sold for a mere $20,000 at a yearling sale. Then Glatt paid $150,000 for the horse at a 2-year-old-sale, and the Marons and Norman Stables formed the ownership team. Still, it was no shock on Nov. 22, 2025 when So Happy went off as a 38-1 longshot at Del Mar Race Track in his racing debut. Mike Smith, a 60-year-old Hall of Fame jockey, was aboard the horse.All I had to do was point him in the right direction, Smith told USA TODAY Sports. When I told him to go, man, he went.So Happy won the race. Now he's won three of his four races and is coming off his most impressive victory yet.It always seems like (a horse) comes around that doesn't have that regal blood or that big breeding, Smith said. And he's one of them, man.'Grandpa' in the stirrupsSmith, the 60-year-old jockey, said hes never considered retiring, even when fellow jockeys needle him, calling him grandpa.He keeps himself in prime condition, Glatt said. And especially in a race like the Derby, how do you replace the experience that a rider likeMike Smithhas?Smith won the 2005 Kentucky Derby onGiacomo, a 50-to-1 longshot. And in 2018, he was 52 when he rode Justify to victory at the Kentucky Derby and went on to win the Triple Crown.Now Smith has a chance to etch his name into the history books.Bill Shoemaker, the late Hall of Fame jockey who was 54 when he rode Ferdinand to victory at the 1988 Kentucky Derby, remains the oldest winning jockey in the race's history. Smith would break that record on May 2 in the "Run for the Roses.''"It might be a record that sticks for a while, man,'' Smith said. "These young guys are catching all my other ones. This is one that'd be tough to get.''Of course, So Happy will have to carry Smith across the finish line.I think we're just starting to see the best him, he said.Hope attached to So HappyMiller, the 94-year-old breeder, said he has gathered with his children and grandchildren to watch So Happys races and thinks about his late wife. He also said he has stayed in touch with Glatt during So Happys ascent.Every time he's won, I've emailed (Glatt) and he's emailed me back, Miller said.Last week, Glatt met Sander Blanco, a 28-year-old horseman from Venezuela. Blanco bought So Happy for $20,000 at a yearling sale and worked with the horse for a year before Glatt bought him for $150,000. They posed for a photo, and Blanco draped his right arm around Glatt's shoulders and smiled. Glatt showed little emoton.After So Happys final workout at Santa Anita last week, the trainer retreated to the office at his barn. He talked about dealing with grief and So Happy.Theres a lot of hope attached to him, theres a lot of emotion attached to him, Glatt said. From the person that bought him and sold him, to me as we try to move forward with our lives, my family and I.At 152nd-running of the Kentucky Derby, there will be a favorite, longshots and stories attached to all of the horses. But there will be only one So Happy.Hell be running for more than roses.This article originally appeared on USA TODAY: Kentucky Derby horse at center of heartbreaking, heartwarming story