conspiracy theorist

noun

1. One who believes in, follows, or advances a conspiracy theory.

   “Mike's a conspiracy theorist; he thinks NASA faked the moon landings.”

   “And you may have noticed that those who are too quick to shout 'conspiracy theorist' are equally swift, when consequences for authority and consensus impend, to look serious and say 'It's more complicated than that.' These have become standard damage-control reflexes.”