Never, perhaps, has an heir been more ready for the crown.

Charles, the eldest son of Queen Elizabeth II and a man born to be king, acceded to the throne Thursday after being the designated successor for longer than anyone in the history of the British monarchy. As King Charles III, he will become sovereign of the world’s most important constitutional monarchy, head of the most storied royal family and a symbol of continuity in a storm-tossed country.

Having aged from an awkward, self-doubting young man into an unhappy middle-aged husband, Charles has become, at 73, a self-assured, gray-haired eminence, steeped in causes like climate change and environmental protection, which were once quirky but now seem peculiarly in sync with the times.