There are many famous horses: Man o' War, Seabiscuit, Secretariate, the Black Stallion, Black Beauty, etc. They'd be famous because, for the first three, they were the fastest race horses in their time. For the last two, authors wrote about them and put their character into words and a book that many people of all ages could read about.
The most famous Quarterhorse halter horse is probably "Impressive"
Apparently the most famous breed of horse is the beautiful Arab.
it is the name of a famous race horse. A movie was made about this horse.
the Clydesdale
secretariat
Secretariat/Red
Thoroughbred horse
Thoroughbreds are one famous breed from England.
Pegasus. the most famous winged horse in mythology
That really depends on where you're from and where you live. In North America, likely the most famous breed of horse would be the American Mustang, followed by the American Quarter Horse. In the Middle East, the most famous breed would be the Arabian horse.
Arion is another kind of horse
The Tennessee Walking Horse