Final answer:
At his first Parliament, Henry IV claimed descent from Henry III, Henry of Guise, and Henry of Navarre. He joined the Roman Catholic Church and issued the Edict of Nantes granting religious toleration to French Protestants.
Step-by-step explanation:
At his first parliament, Henry IV claimed descent from Henry III, Henry of Guise, and Henry of Navarre. The War of the Three Henrys resulted in the deaths of two of the Henrys, leaving only Henry of Navarre as the Protestant ruler. After ascending to the throne, Henry IV joined the Roman Catholic Church and issued the Edict of Nantes, granting religious toleration to French Protestants.