2. David Bowie
Though it's clear that David Bowie was fascinated with the idea of extraterrestrials through his innumerable songs referencing life beyond earth (Life On Mars? Loving The Alien, The Man Who Fell To Earth... to name merely a few), what many don't know is this conviction ran quite a bit deeper. In the book Laugh Gnostic by author Peter Koenig, Bowie is quoted as detailing an experience he had while travelling through the English countryside with a friend. Both noticed a strange object hovering above a field, which Bowie believed may not have been a physical object but an extraterrestrial doorway into a dimension beyond our own. If that's not curious enough, there are conspiracy theorists out there who actually believe Bowie himself is an alien.
Feel free to judge the legitimacy of such claims yourself.