Complex sentence: Kilmer was the breeder of Reigh Count, the winner of the 1928 Kentucky Derby, and owner of Exterminator, the winner of the 1918 Kentucky Derby and 1922 American Horse of the Year, and Sun Beau, the largest money maker until Seabiscuit in 1939.
Split into simpler sentences: Kilmer was the breeder of Reigh Count, the winner of the 1928 Kentucky Derby. He was the owner of Exterminator, the winner of the 1918 Kentucky Derby and 1922 American Horse of the Year, and the breeder and owner of Sun Beau, the largest money maker until Seabiscuit in 1939.