The senior scientist, who used to work at Area 51 himself, opened up about his career in studying UFOs and alien life at the secretive base in a documentary filmed just before he died.
He explained: "There are two groups of aliens.
"They divide them into two groups. It’s like a cattle ranch."
He described the aliens as being five foot tall, revealing: "One group are wranglers, and the others are rustlers – the stealers of cattle.
"The ones that are wranglers are much more friendly, and have a better relationship with us."
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He added that "one or two of them are around 230 years old" and that "at least 18 operate with our facility" at Area 51.
Dr Boyd, who said that the aliens are dressed in dungarees so they can be grabbed when they start to float, can communicate with humans via telepathy.
He revealed: "They're able to use their own voice by telepathy to talk to you."
Watch the full documentary for yourself below:
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