Who was Gustav Steinbrecht and what did he contribute to dressage?

Gustav Steinbrecht was a German equestrian master who lived from 1808 to 1885 and whose posthumously published work Gymnasium of the Horse — completed by his student Paul Plinzner from Steinbrecht's notes after his death — remains the most comprehensive and systematically organized text of the German classical tradition and one of the most influential books in the history of dressage training. Steinbrecht's contribution was primarily the synthesis and systematic organization of the principles that the German training tradition had been developing — taking the insights of de la Guérinière, the German military riding tradition, and his own extensive practical experience and organizing them into a complete training system that addressed the development of the horse from its earliest training through the highest movements of classical dressage. His famous dictum — ride your horse forward and make it straight — captures in a few words the essential principle of correct training that all of the Gymnasium's detailed systematic instruction ultimately serves, and remains one of the most frequently quoted formulations of the training principle that impulsion and straightness are the foundations on which all collection must be built. Steinbrecht was deeply concerned with the relationship between correct training and the horse's physical health, and his discussions of the musculoskeletal development that correct training produces versus the physical damage that incorrect training causes reflect a level of anatomical understanding that was sophisticated for his era and that anticipated the biomechanical approach to equine training that contemporary equine science has developed. His influence on the German training tradition — which has dominated international dressage competition for much of the sport's modern history — is pervasive and direct, with the German National Equestrian Federation's training scale and systematic approach reflecting Steinbrecht's organizing principles.