A Filipino historian focusing on the early Spanish colonial history in the Philippines, he wrote numerous books and articles on various aspects of national and local histories. As a Magellan scholar, he authored Ferdinand Magellan: The Armada de Maluco and the European Discovery of the Philippines, acclaimed by both Filipino and foreign scholars as one of the most authoritative works on the subject. A lecturer in numerous national and international conferences in history, he is also a member of Philippine and European committees on the Magellan celebration and an accomplished historical painter.