Which Govt. Scientists, Astronauts, or Cosmonauts have publicly admitted knowledge of alien presence?

Dr. Mitchell is a very accomplished man, but frankly has been making incredible claims for years without backing them up - psychic abilities exist, paranormal stuff happens all the time, this alien thing is just the latest unverifiable claim. It's only getting attention because he went into space - but you don't have to be an expert at astronomy or even that knowledgeable about it to become an astronaut, and it's obvious this is a problem here.