Buzz Aldrin is an American astronaut who walked on the Moon during the Apollo 11 mission in 1969, stepping onto the surface just after his crewmate Neil Armstrong — and privately took Holy Communion there, the first religious ceremony ever held on another world. Before joining NASA he was a fighter pilot and earned a doctorate studying how spacecraft meet up in orbit, ideas that were used on real Moon missions. He has spent the decades since encouraging space exploration, especially the dream of sending people to Mars.