The Rocky Mountain Horse is a horse breed developed in the state of Kentucky in the United States. Despite its name, it originated not in the Rocky Mountains, but instead in the Appalachian Mountains. A foundation stallion, brought from the western United States to eastern Kentucky around 1890, began the Rocky Mountain type in the late 19th century. In the mid-20th century, a stallion named Old Tobe, owned by a prominent breeder, was used to develop the modern type; today most Rocky Mountain Horses trace back to this stallion. In 1986, the Rocky Mountain Horse Association was formed and by 2005 has registered over 12,000 horses. The breed is known for its preferred "chocolate" coat color and flaxen mane and tail, the result of the relatively rare silver dapple gene acting on a black coat, seen in much of the population. It also exhibits a four-beat ambling gait known as the "single-foot". Originally developed as a multi-purpose riding, driving and light draft horse, today it is used mainly for trail riding and working cattle.

The silver or silver dapple (Z) gene is a dilution gene that affects the black base coat color and is associated with Multiple Congenital Ocular Abnormalities. It will typically dilute a black mane and tail to a silvery gray or flaxen color, and a black body to a chocolaty brown, sometimes with dapples. It is responsible for a group of coat colors in horses called "silver dapple" in the west, or "taffy" in Australia. The most common colors in this category are black silver and bay silver, referring to the respective underlying coat color.