Complex sentence: Laffit Pincay began his riding career in his native Panama until 1966 when horseman Fred W. Hooper and agent Camilo Marin sponsored him to come to the United States and ride under contract.
Split into simpler sentences: Laffit Pincay began his riding career in his native Panama. In 1966, prominent horseman Fred W. Hooper and agent Camilo Marin sponsored him to come to the United States and ride under contract.