Edgar Mitchell
In 1971, Mitchell became the sixth person to walk on the moon.
But he spent the rest of his life convinced that “aliens have been observing us and have been here for some time”.
He once claimed that peace-loving aliens had visited Earth on a mission to save humanity from nuclear war and suggested the Vatican knows the truth about the existence of extraterrestrials.
Mitchell also alleged that UFOs had been seen above nuke bases and often disabled the missiles held within Cold War-era weapons silos.
The spaceman firmly believed the American government covered up the famous Roswell incident in 1947, when a flying disc allegedly crashed near a small town in New Mexico.
“The reason for the denial is they didn’t know if they [the aliens] were hostile and they didn’t want the Soviets to know so they devised to lie about it and cover it up,” he reportedly said.
Gordon Cooper
Cooper was one of the seven astronauts who took part in Project Mercury, the first American manned mission which ran from 1958 until 1963.
The craft he piloted was dubbed "spam in a can" because it was automatically controlled, rather than piloted by the astronauts on board.
But even before he underwent the life changing experience of becoming the first man to sleep in space, he claimed to have seen UFOs flying over Germany in 1951.
The spaceman also said he saw flying saucers spying on a secret airbase where experimental American aircraft were being tested.
“I believe that these extraterrestrial vehicles and their crews are visiting this planet from other planets, which are a little more technically advanced than we are on Earth," he told the UN in 1984.
"We may first have to show them that we have learned how to resolve our problems by peaceful means rather than warfare, before we are accepted as fully qualified universal team members.
"Their acceptance will have tremendous possibilities of advancing our world in all areas."