Tucker Carlson thinks they're biblical entities. Others say they are humans from the future coming back to study us.
Now, a new film proposes an even stranger theory about UFOs.
The Cosmic Jokerinvestigates the idea that these entitiesmay be 'tricksters' that deliberately shape themselves into what people want to see or into forms that people may be familiar with,director Mark Christopher Lee told DailyMail.com.
The movie concentrates on two infamous alien encounter tails: the Robert Taylor incident and thePascagoula abduction of fishermen Charles Hickson and Calvin Parker.
The Pascagoula abduction of fishermen Charles Hickson (left) and Calvin Parker (right) and occurred in 1973
Mr Hickson and Mr Parker reportedbeing experimented on by aliens with crab-like claws
It asks the question: Did the aliens who made contact with the men deliberately shape shift themselves into forms reminiscent of something in their personal lives?
The film also suggests aliens might not be from space at all - and that this might be behind alleged cover-ups of UFO evidence.
Mr Taylor was a forest worker in Scotland who described seeing a UFO resembling a naval sea mine in 1979.
The Cosmic Jokersuggests the entity deliberately take this form to resemble something Mr Taylor was familiar with from his time in the military.
In 1973 in Pascagoula, Mississippi, Mr Hickson and Mr Parker reportedbeing experimented on by aliens with crab-like claws.
Didalienintelligence shape itself to a form familiar to the two Deep South fishermen?
Lee told DailyMail.com: ‘What piqued my interest for this film was interviews about the Pascagoula Encounter in the US in 1973. Calvin Parker and Charles Hickson had an alleged abduction experience whilst fishing near the Pascagoula River.
‘They claimed they were taken onboard an alien craft and examined and physically handled by two aliens which had crab-like pincers. I just thought - why would the aliens have crab like pincers?’
The two men reported to the sheriff's department they had been abducted by gray-skinned aliens while fishing - with the aliens having ‘crab-like’ hands and ‘robotic’ mouths.
The men each had a puncture wound in their arm.
Hickson told The Washington Post: 'I was just getting ready to get some more bait, when I heard a kind of zipping sound. I looked up and saw a blue flashing light. Calvin turned around too.
'We saw a 30-foot-long object with a little dome on top.'
The two Pascagoula witnesses had physical injuries from the encounter
The police officers interviewing the men secretly left a tape recorder in the room with the witnesses after law enforcement left.
While they may have been hoping to catch the men drop their act and admit they made up the encounter, they only recorded them saying the experience scared them to death.
Lee told this website: ‘The police placed a hidden tape recorder, which captured them talking about how the experience scared them out of their lives. So that begs the question: if the experience was real, what were these creatures?
'Did they actually adapt themselves to what a couple of Deep South fishermen might expect to see? Why did they see the same thing?’
In the film, Lee also speaks to UFO author Malcolm Robinson, who describes the strange encounter World War II veteran Mr Taylor had with a UFO in the Dechmont Woods in Scotland.
Lee told DailyMail.com: ‘Mr Taylor encountered and was attacked by an alien or intelligence that was similar in appearance to a naval sea mine with sharp protruding limbs coming off the sides.
'Again I thought did the intelligence, whatever it may be, take this from as it would be familiar to Robert Taylor having served in the military?’
Mr Taylor's reported sighting was investigated by police after two spiked spheres rolled at him - leaving him unconscious for 20 minutes with ripped clothing.
Ddirector Mark Christopher Lee spoke to DailyMail.com
The war hero and churchgoer was believed by locals - and police found strange marks on the ground which could not be explained by machinery in the vicinity.
Lee said others have suggested Taylor’s encounter may have been triggered by an epileptic episode.
The idea of aliens as shape-shifting ‘tricksters’ was first proposed in a book by late author John Keel, whose work inspired the Richard Gere film The Mothman Prophecies, Lee told this website.
He said: ‘Keep was the first to really study in minute detail UFO and alien encounters. From his research he noted that there was always this mischievous trickster element in these sightings.’
Keel’s book suggests aliens may not be from other planets, or from space at all - but may instead be ‘ultra-terrestrials’ who manipulate human beliefs.
Lee added: ‘Of course if this theory is true it is probably far more disturbing than being visited by other beings from other planets.
'Are we as humans the playthings of a far superior intelligence that lives alongside us?
‘Some modern Ufologists like Blink 182 musician Tom DeLonge believe that this intelligence has always been with us and that the US government knows this and is using the extraterrestrial hypothesis as a smokescreen to divert the public from the wilder truth.’
The Cosmic Joker is out now on Tubi TV.
