Exterminator (May 30, 1915 - September 26, 1945) was an American Thoroughbred racehorse and the winner of the 1918 Kentucky Derby, and in 1922 won Horse of the Year honors. The lanky chestnut colt was bred by F. D. "Dixie" Knight (Mrs. M.J. Mizner, Knight's mother, was said to be the actual breeder) and foaled at Almahurst Farm near Lexington, Kentucky. Exterminator was sired by McGee who also produced Donerail, the winner of the 1913 Kentucky Derby. At the Saratoga Paddock sale of 1916, he was bought as a yearling for $1,500 by J. Cal Milam who trained his own horses. The big colt grew fast, reaching 16.3 hands at two but he was awkward and coarse looking. For this reason, Milam had him gelded. On June 30, 1917 at Latonia Race Track in Covington, Kentucky, Exterminator made his debut in a six-furlong maiden race that he won by three lengths. Sent to race in Windsor, Ontario, Canada, he suffered a muscle sprain and Milam gave him time off to grow into his size, which by now was 17 hands. Still, he had earned $1,500 and a potential nomination to the Kentucky Derby.