U.S. Marine Corps aviator and Mercury astronaut, the first American to orbit Earth (Friendship 7, February 1962). Reported unexplained luminous 'firefly'-like particles during the flight, later explained by NASA as frozen condensation vented from the capsule. Referenced the episode comedically in a 2001 'Frasier' cameo.
John Glenn served as a U.S. Marine Corps combat pilot in the Second World War and Korea before joining NASA's original Mercury Seven astronaut corps. On his February 1962 Friendship 7 flight, the first orbital spaceflight by an American, he radioed that he was passing through 'a big mass of thousands of very small particles' glowing like fireflies, which briefly puzzled ground control. Fellow astronaut Scott Carpenter's subsequent flight helped confirm the particles were ice crystals vented from the spacecraft rather than an anomalous phenomenon. Glenn went on to serve 24 years as a U.S. Senator from Ohio and returned to orbit in 1998 aboard the Space Shuttle Discovery (STS-95) at age 77. In 2001 he appeared as himself in a comedic 'Frasier' episode that played on UFO-conspiracy tropes, including his own 'fireflies' story.