Who served as the chief rider of the Russian Cavalry School and created a popular stirrup design?

The correct answer is James Fillis, who is recognized for his significant contributions to riding and equestrian education. As the chief rider of the Russian Cavalry School, he played a pivotal role in advancing cavalry techniques and training practices during his time. One of his notable achievements was the creation of a stirrup design that gained popularity among horse riders. Fillis's emphasis on the practical aspects of riding, alongside his innovative design, contributed to improvements in the comfort and effectiveness of riders, influencing riding standards well beyond his own era.

The other individuals listed have made their mark in different areas of equestrianism but are not associated with the same contributions regarding the Russian Cavalry School or the specific stirrup design mentioned. For example, Federico Caprilli is known for his development of the modern riding style and jumping technique, while Alfred Kerdiles is celebrated for his work in training methods. Harold B. Linscott, on the other hand, was noted for his advancements in horse show rules and regulations rather than for riding school leadership or stirrup design. Thus, Fillis stands out with his unique blend of both riding expertise and innovation.