Wikipedia: "Ancient aliens" refers to a pseudoscientific hypothesis, that intelligent extraterrestrial beings visited Earth and made contact with humans in antiquity and prehistoric times.

Dr. Michael S. Heiser talks about alien abduction, Zecharia Sitchin, ancient aliens and how no archaeologist or researcher takes them seriously.

Although Dr. Michael S. Heiser doesn't say it out loud the reason he had to start another channel in Vimeo away from Youtube is probably because of copyright infringement notices aka harassment from Ancient Aliens gang.