Final answer:
Prince Henry the Navigator initiated the Portuguese colonial expansion in the Gulf region and was instrumental in the early period of Atlantic exploration.
Step-by-step explanation:
The Portuguese colonial expansion in the Gulf region and beyond was initiated by Prince Henry the Navigator, who was the third son of John I, king of Portugal. Prince Henry was instrumental in advancing the era of Atlantic exploration, establishing a navigation school, and promoting exploratory voyages along the coast of Africa and across the Atlantic Ocean.
The Portuguese exploration efforts under his guidance led to significant discoveries, including the Madeira Islands, and set the stage for future expeditions by other Portuguese explorers such as Vasco da Gama and Bartolomeu Dias.
To address the specific question, the Portuguese colonial expansion in the gulf region was started by Prince Henry the Navigator (Option A).