The most famous Quarterhorse halter horse is probably "Impressive"
Apparently the most famous breed of horse is the beautiful Arab.
The most famous Quarter Horse in the world is Doc Bar.
The Clydesdale is a breed of horse.A breed of horse is a classification of a type of horse that has recurring genetic features and most or all of that type can trace back to one or several foundation ancestors.
The most popular type of horse is the quarter horse, because it can run in races
"Most famous" is relative. Secratariat was special, because he was just a regular horse. No famous sire, no extra famous breeder. He was the horse that represented the people. Little known fact: Secratariat suffered constantly from laminitis.
A rocking horse.
There are so many really famous Quarter Horse stallions I know of, but I would say Impressive is probably one of the most famous ones.