Final answer:
The French explorer who explored the St. Lawrence River and established the settlement of Quebec was Samuel de Champlain.
Step-by-step explanation:
The French explorer who explored the St. Lawrence River and established the settlement of Quebec was Samuel de Champlain. In 1608, Champlain built a fort at Quebec, which became the first major French settlement in North America. He played a crucial role in establishing the French presence in the New World.