I don't think that aliens or UFOs exist.
I do believe there are other "intelligent" beings out there, but those would be angels, cherubims, and the sort.
You know, these days, people talk about seeing aliens and weird human like creatures. But a few thousand years ago, and people were speculating that they saw monsters and gods (think almost any mythology). I personally think that maybe mythology was inspired by peoples sightings of angels and cherubim. I'm just a highschooler though, who hasn't done any deep research into such things, just maybe some ideas about why people come up with what they think they saw.