Astronaut John Glenn poses, on January 20, 1962 during a training session before his 20 February 1962 NASA's Mercury program space flight aboard in the Mercury capsule Friendship 7 in which he became the first American to orbit the Earth. AFP PHOTO / NASA

John Glenn, who became one of the 20th century's greatest explorers as the first American to orbit Earth and later as the world's oldest astronaut, and also had a long career as a U.S. senator, died in Ohio on Thursday at age 95.