A foundation stallion, brought from the western United States to eastern Kentucky around 1890, began the Rocky Mountain type in the late 19th century.

The physical characteristics are somewhat variable, due to the disparate breeds that created the Rocky Mountain Horse.

MCOA is characterized by the abnormal development of some ocular tissues, which causes compromised vision, although generally of a mild form; the disease is non-progressive.

American Saddlebreds, Tennessee Walking Horses and Missouri Fox Trotters also originated in the same general geographic area, from the same mixing of Spanish and English blood.

Brought to the area as a colt, oral histories state that the "Rocky Mountain Horse", as he was known, possessed the preferred chocolate color and flaxen mane and tail found in the breed today, as well as the single-foot gait.

[12] This foundation stallion produced a descendant, named Old Tobe, who became the more modern father of the Rocky Mountain Horse breed.

For most of the 20th century, Tuttle was a prominent breeder of Rocky Mountain Horses, and helped to keep the strain alive during the Great Depression and World War II.

After World War II, despite declining horse populations in the US, Tuttle kept his herd, and continued to use Old Tobe as a breeding stallion.

Horses must also, after reaching 23 months of age, be inspected to ensure that they meet the physical characteristic and gait requirements of the registry.

[13] The breed was originally developed for general use on the farms of the Appalachian foothills, where it was found pulling plows and buggies, working cattle and being ridden by both adults and children.