1. King Charles III

Age at accession: 73 years, 9 months, 6 days.

Reign: 2023–

The oldest son of Queen Elizabeth II, Charles was the longest heir apparent, waiting in the wings while his mother became the longest-serving monarch in English history. As he waited, he entered the Royal Air Force and then the Royal Navy. He served for five years, training as a helicopter pilot and sailing aboard a guarded missile destroyer. He also participated in parachute training. Since his early years, Charles has embraced charitable activity and giving, lending his support to hundreds of charities. He recently was the first U.K. patron of the International Rescue Committee, a charity that helps refugees displaced by wars or natural disasters. One of his most passionate projects has been to champion protection of the environment. He has embraced organic farming and has been an outspoken critic of activities that have led to global warming. In 2007, he launched the Prince's Rainforest Project, a worldwide program to stem the tide of tropical deforestation. He also, in 2021, launched Terra Carta, an initiative to encourage sustainable finance among the world's leading economies.