Caractacus, 
a descendant of the Godolphin Arabian.
LBJ
With his Texas drawl, boots and bolo tie, LBJ always seemed much more suited to life on the ranch than life in Washington.Zachary Taylor
When the former Major General of the US Army moved into the White House, he took his beloved warhorse Old Whitey with him. It's said that Old Whitey would often graze in the White House lawn and it was common for visitors to pluck a hair or two for a lovely parting gift. 5. Andrew Jackson Old Hickory had a famous thirst for gambling and bred his own racing horses on his Tennessee estate, the Hermitage. When he left Nashville for Washington he brought his stables with him, and the White House actually became a fully functioning breeding, training and racing operation. Awesome.Ronald Reagan
Courtesy of the Ronald Reagan Foundation and Library Though he played one in the movies, Reagan was quite the cowboy himself and without question the most equine adept modern President. He rode in the cavalry and was so advanced in the saddle that when he would sneak out for rides while in office, the secret service struggled to find a suitable agent with the ability keep up.Ulysses S. Grant
Grant is considered by some to be the greatest pure equestrian to ever hold the ultimate office. His natural touch and feel with horses was evident from an early age and his riding ability made him a standout at West Point and later the US Army he would eventually control. He was known as a fearless rider in the saddle who could break even the most fiery of colts. Grant's most famous horse, Cincinnati, was the son of the great thoroughbred stallion Lexington, and was his preferred means of transportation during the Civil War.Teddy Roosevelt
While many Presidents were accomplished riders and breeders, no one embraced the horsemen life quite like Teddy. His rugged cowboy persona was more than just political posturing, it embodied what he called his approach to “the strenuous life.” In 1898, he helped establish the 1st United States Volunteer Cavalry, famously known as the Rough Riders, to assist in the Spanish-American War. Even while in office, Roosevelt did not neglect his cowboy ways. When White House officials tried to give him an automobile for state duties, he famously refused: “The Roosevelt's are horse people,” he remarked. Damn right, Ted. Roosevelt was so serious about his riding that anyone invited to accompany him on the trails was given a printed copy of his Rules of the Road. Here they are, courtesy of the White House Historical Association: Roosevelt's Rules of the Road: First: The president will notify whom he wishes to ride with him. The one notified will take position on the left of the president and keep his right stirrup back of the president's left stirrup. Second: Those following will keep not less than ten yards in the rear of the president. Third: When the president asks anyone in the party to ride with him the one at his side should at once retire to the rear. Salutes should be returned only by the president, except by those in the rear. Anyone unable to control his horse should withdraw to the rear.