Robert "Bobby" Costello started as the U.S. Eventing Team Chef d'Equipe and Technical Advisor for the program in 2022. With a decorated career as an international athlete, actively competing up until 2010, Costello was a member of the World Championship Team and placed in the top 10 as an individual at the Sydney Olympic Games in 2000. As the U.S. Technical Advisor, Costello led the U.S. Eventing Team to several key championship results, including a team silver at the 2022 FEI World Eventing Championships in Pratoni del Vivaro Italy and a team silver at the 2023 Pan American Games in Santiago, Chile.  

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. 

Boyd Martin, the son of Olympic speed skater Toy (Dorgan) Martin and Olympic cross-country skier Ross Martin, began riding at a young age in his native country of Australia. He made his debut at the CCI5*-L with a win at the 2003 Australian International Three-Day Event riding the Thoroughbred gelding True Blue Toozac.

He moved to the U.S. in 2007 to further his career as an eventing professional, serving as the assistant trainer to Olympian Phillip Dutton for two years before starting his own business. Martin began riding for the U.S. in 2009.

Martin is a three-time Olympian, having represented the U.S. in London 2012, Rio de Janeiro 2016, and Tokyo 2020. He is a four-time U.S. Eventing Team member for the FEI Eventing World Championship, including as a part of the silver medal-winning team in 2022 in Pratoni, Italy. With Pancho Villa, he was a member of the U.S. team that won gold at the 2015 Pan American Games, and in 2019, he won team and individual gold at the Pan American Games with Christine, Thomas, and Tommie Turner's Tsetserleg TSF.

Twice, Martin has been the USEF CCI5*-L Eventing National Champion at the Kentucky Three-Day Event. First in 2019 with Tsetserleg TSF and again in 2021 with Christine, Thomas, Tommie, and his own, On Cue. In October 2021, he won the inaugural Maryland 5 Star with On Cue, becoming the first American to win a CCI5* since 2008.

In 2023, Martin piloted his string to several significant top finishes at the CCI5*-L with five top-ten finishes at events around the world, including two top-ten finishes for Fedarman B at both Luhmuhlen and Pau. Martin brought both Fedarman B and Commando 3 forward as potential Olympic selections at the start of the 2024 season. A strong showing of both at the CCI4*-S at the 2024 Kentucky Three-Day Event did not make selection easy, but Martin ultimately chose Fedarman B as his mount of the 2024 Olympic Games, with Commando 3 as a direct reserve. Paris 2024 will be Martin's fourth consecutive Olympic appearance for the U.S. Olympic Eventing Team. 

Martin and Fedarman B were successful in Paris, adding just 1.6 to their initial dressage score of 30.5. The duo were one of only seven combinations to jump clear in both rounds on the final day, finishing tenth individually and contributing to the team's sixth place. 

In 2025, Martin helped the Defender U.S. Eventing team secure a second-place finish for the third consecutive year at the CHIO Aachen CCI4*-S and later that fall, earned the first ever title as winner of the Inaugural US Equestrian Open of Eventing Final held at Morven Park. Martin also placed on the podium at every CCI5*-L entered in 2025 and subsequently was named the 2025 World Equestrian Brands USEA Rider of the Year. 

The 2026 season started strong for Martin with a podium finish aboard Commando 3, owned by Yankee Creek Ranch, at the Bouckaert CCI4*-S. Martin then claimed a second and third-place finish on Miks Master C, owned by OHP Hammertime Partners, and Shanroe Cooley, owned by Dallas LLC, at the Fair Hill International CCI4*-S the following month. In April 2026, Martin had two strong finishes with Commando 3 and Cooley Nutcracker at the Defender Kentucky Three Day Event CCI5*-L, earning sixth place with Commando 3, and finishing just outside of the top ten with Cooley Nutcracker, owned by Liz’s Nutcrackers.  The following month, Martin and Shanroe Cooley took home third in the Tryon International CCI4*-S before making their first 5* appearance at the Longines Luhmühlen Horse Trials in June coming home with yet another podium finish, earning third place overall.  

Martin and his wife, professional dressage trainer and athlete, Silva Martin, own and operate Windurra USA in Pennsylvania.

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. 

With over 60 FEI starts in 2025, and an impressive 21 podium finishes, one of the major highlights of Pamukcu’s season was helping the Defender U.S. Eventing Team take silver at the CHIO Aachen CCIO4*-S with her longtime partner, HSH Blake owned by, Mollie Hoff, Sherrie Martin, and Caroline and Deniz Pamukcu. The following month, Pamukcu secured a top twenty finish individually and contributed to the Defender U.S. Eventing Team’s silver medal at the Arville CCIO4*-NC-S with She’s The One, owned by Andy and Mollie Hoff, Sherrie Martin and Caroline Pamukcu. Later that fall, Pamukcu finished third in the US Equestrian Open Eventing Series and went to take fourth overall with HSH Double Sixteen, owned by Double Sixteen Partnership, in the US Open Eventing Final CCI4*-L at Morven Park International. To conclude their 2025 competition season, Pamukcu piloted HSH Blake in his first CCI5*-L at the MARS Maryland 5 Star at Fair Hill where the pair came home with a strong fourth-place finish.  

Pamukcu and her team continued to showcase their consistency and strength in 2026 with a win at the Bouckaert Equestrian H.T. International CCI4*-S aboard HSH Connor, owned by Sherrie Martin, Luann McElduff, and Caroline Pamukcu. Just a short month later, Pamucku secured her tenth US Open Qualifier win with HSH Double Sixteen at the Fair Hill International CCI4*-S as the only combination to go double clear in the cross-country phase.  

Entering the Defender Kentucky Three-Day Event CCI5*-L with a strong spring season, Pamukcu doubled down with a second-place finish with HSH Blake, earning Defender/USEF CCI5*-L National Reserve Champion honors in her highest-ever finish at the event. Pamukcu’s talent continued to shine at the MARS Bromont CCI Three Day Event with two podium finishes in the CCI4*-L with She’s The One and HSH Double Sixteen.  

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.