Final answer:
Marie de Medici, the daughter of Francis de Medici of Tuscany, was the powerful French duchess who married King Henry IV of France, bringing substantial wealth to the French crown and serving as Regent Queen after her husband's assassination.
Step-by-step explanation:
The powerful French duchess who married Henry II was Marie de Medici. Originating from a prestigious lineage, Marie de Medici was the daughter of Francis de Medici of Tuscany. Her marriage to King Henry IV of France in 1600 was not only a significant political alliance but also brought substantial wealth to the French crown. Marie’s dowry alone was influential enough to alleviate a significant portion of France’s national debt. After Henry IV’s assassination in 1610, Marie served as the Regent Queen of France, governing on behalf of her son Louis XIII until he reached the age of majority. Despite this powerful role; Marie de Medici's reign encountered many challenges, including resistance from nobility and conflict with her own children.