Robert "Bobby" Costello started riding in as a child in Massachusetts, competing at local shows and fox-hunting with the Myopia Hounds. He found the sport of eventing and worked his way through the ranks as a professional, ultimately competing at the highest levels in the sport of eventing.

Costello became an upper-level staple for the program, representing the U.S. Eventing Team at the 2000 Sydney Olympic Games in Sydney Australia, taking eighth individually with Chevalier. The pair also secured top results at Bughley CCI5*-L and the Rolex Kentucky Three-Day Event. Costello finished seventh individually at the 2003 Pan American Games with Dalliance, before turning towards coaching and eventually stepping away from riding full-time in 2010 and focusing solely on coaching and training. 

Since he joined the program in 2022, Costello has helped several senior teams produce significant results at major international competitions and championships including a team silver at the 2022 FEI Eventing World Championships in Pratoni del Vivaro, Italy, and a team silver at the 2023 Pan American Games in Santiago, Chile. Under Costello's tutelage, the team has also secured two-consecutive second-place finishes in the CCIO4*-S at CHIO Aachen in 2023 and 2024. 

Sydney Elliott made her debut at the CCI5*-L level in 2016 when she completed the Rolex Kentucky Three-Day Event with Cisko A. The pair went on to represent the U.S. on the Nations Cup Team at Great Meadow International in 2018, and had top-ten finishes in the CCI4*-S at the Carolina International, Chattahoochee Hills CCI4*-S, Stable View Oktoberfest CCI4*-S, and Fair Hill International CCI3*-L that same year.

With QC Diamantaire, Elliott has had top-ten finishes in the 2020 USEF CCI4*-L Eventing National Championship at Tryon, 2021 Pine Top Advanced Horse Trials, 2021 Carolina International CCI4*-S, 2021 The Fork @ TIEC CCI4*-S, and 2022 Land Rover Kentucky Three-Day Event CCI5*.

Elliott and "Q" have represented the U.S. Eventing Team at FEI Nations Cup comptetitions including in 2022 in the CCIO4*-S at CHIO Aachen and in 2021 at CCIO4*-L at Boekelo, where they finished fifth individually and led the U.S. team to a silver medal.

In 2023, Elliott and Q were part of the silver medal-winning U.S. Eventing Team at the Pan American Games in Santiago, Chile, where they finished eighth individually. The pair were also named as traveling alternates for the 2024 Paris Olympic Games, where they were called into the team as the traveling reserve after the withdrawl of Diabolo. 

California-born Elisabeth “Liz” Halliday began riding when she was 8 years as an active member the United States Pony Club. Halliday moved to England in 2000 to work for famed eventer William Fox-Pitt and was based in Europe for many years before bringing her operation to the U.S. with locations in Ocala, Florida, and Lexington, Kentucky, in 2020. That same year, she earned the distinction of USEA Rider of the Year after racking up nine wins and 23 total top-ten finishes at FEI competitions over the season.

Halliday achieved her first CCI5*-L completion in 2016 at the Kentucky Three-Day Event with Deborah Halliday's HHS Cooley. She has also brought numerous horses to top-ten finishes at the level, including Ocala Horse Properties, LLC's Deniro Z, The Monster Partnership's Cooley Quicksilver, and The Nutcracker Syndicate's Cooley Nutrcracker.

In 2023, she brought Deborah Palmer's and Ocala Horse Properties, LLC's Miks Master C to his CCI5*-L debut at the Kentucky Three-Day Event where they finished in third-place overall and were reserve champions in the USEF CCI5*-L Eventing National Championship. In 2023, the pair were the Adequan USEA Advanced National Champions at the American Eventing Championships.

Halliday has represented the U.S. Eventing Team in several FEI Nations Cup competitions, including the 2022 CCIO4*-S at Bromont in Canada, where she rode Miks Master C to individual victory and led the U.S. team to secure the win. In 2023, the pair were part of the silver medal-winning team at the Pan American Games in Santiago, Chile.

Halliday continued her consistency in 2024, marking several top results with both Cooley Nutcracker and Miks Master C, with a top-ten finish coming for Cooley Nutcracker at the Kentucky Three-Day Event CCI5*-L in April. The pair were called onto the U.S. Olympic Eventing Team for the Paris 2024 Olympic Games where they helped the team finish sixth overall and 19th individually. 

In addition to her equestrian pursuits, Halliday was a professional driver in sportscar and GT endurance disciplines, competing from 1997 to 2010 before focusing on her equestrian career. 

Caroline Pamukcu (neé Martin) is a talented young professional who has steadily risen through the USEF Eventing High Performance ranks throughout her career. Pamukcu earned her first international medal in 2013, as the Young Rider individual and team gold medalist in 2013 riding Quantam Solace, her Argentine Sport Horse. 

Pamukcu has represented the U.S. Eventing Team internationally multiple times, including on the second-place teams at the 2022 Houghton Hall (GBR) CCIO4*-NC-S riding Sherrie Martin and her own, Islandwood Captain Jack and the 2023 Strzegom (POL) CCIO4*-NC-S with HSH Blake owned by Caroline and Daniz Pamukcu, Sherrie Martin, and Mollie Hoff. In 2023, Caroline and HSH Blake won individual gold and led the U.S. team to silver at the Pan American Games in Santiago, Chile. 

HSH Blake is a notable product of Pamukcu’s young horse training program. She started competing the 2015 Irish Sport Horse gelding at the novice level in 2020 and in 2022 finished 10^th at the FEI Young Horse World Championship in France. At that same event, she won a silver medal with Sherrie Martin's, Luann McElduff's and her own, HSH Connor who went on to win the 2023 USEF CCI3*-L Eventing National Championship.

The Redfield King's HX Group's 2015 KWPN gelding, King’s Especiale got his start in the show ring as a four year-old with Pamukcu and is now a successful four-star competitor with a second-place finish at the 2023 Morven Park International Horse Trials CCI4*-L and a win in the CCI4*-S at Great Meadow. In 2024, Caroline and King's Especiale were named to the Defender U.S. Eventing Team at the FEI Eventing Nations Cup CCIO4*-NC-S at Millstreet International Horse Trials where they posted the top individual score for the team and assisted in securing a team silver-medal finish. 

With the strong performances of Pamukcu and HSH Blake throughout the 2023 and 2024 season, the pair were named to their first Olympic Team as one of the brightest young combinations for the program. HSH Blake and Pamucku were the first to compete for the team in their Olympic Debut, earning a 30.40 in the dressage phase and finishing on a final total score of 66.8 for 36th place overall and contributing to the team's sixth place finish. 

Pamukcu most recently welcomed her first child with husband, Daniz Pamukcu - a little girl named Blake. 

Sharon White bases her Last Frontier Farm operation out of Summit Point, West Viriginia, and has been a mainstay on the eventing circuit in the U.S. for more than three decades. White began riding as a child, continuously moving through the international ranks throughout her career. She has participated in the Kentucky Three-Day Event CCI5*-L more than ten times with five different horses. She has represented the U.S. internationally at events like Boekelo CCIO4*-L, Pau CCI5*, and Luhmuhlen CCI5*. 

White was listed as an alternate for the 2018 FEI World Equestrian Games in Tryon, N.C., and made her first senior team debut at the 2023 Pan American Games in Santiago, Chile. White and Claus 63 helped the team earn a silver medal and finished tenth individually. White has been named to multiple USEF Eventing High Performance Traning Lists and honored as the receipient of the Rebecca Broussard National Developing Rider Grant in 2011.