In some circles, it's considered the pet animal of alien visitors. Others believe it's the result of a NASA experiment gone wrong. Still other conspiracy theorists say it's the source of the HIV/AIDS virus.
But while stories about the mysterious chupacabra have spread far and wide, real information about a curious-looking creature with that name is virtually nonexistent.
As with Bigfoot, the Loch Ness monster and the other bizarre beasts in urban legends, the tale of the chupacabra thrives on the first-person accounts of people who claim to see it -- and the very active imagination of the public at large.
Now Benjamin Radford, a paranormal investigator and managing editor of Skeptical Inquirer magazine, says he can put the story of the chupacabra to rest. After five years of digging, he said he's uncovered the roots of the mystery.
In his new book, "Tracking the Chupacabra: The Vampire Beast in Fact, Fiction, and Folklore," Radford lays it all out, showing how one woman's story turned into a global sensation.
"What really interested me about the chupacabra is that it's a vampire, unlike Bigfoot, unlike the Loch Ness monster, the moth man, the New Jersey Devil," he said. "Whatever beasties people have laying around, this one sucks blood."
Stories of the chupacabra, which means "goat-sucker" in Spanish, spread mainly in Latin America, the southwestern parts of the U.S. and other Spanish-speaking areas. Many people assume that the phenomenon goes back hundreds of years, Radford said, but it's really only about 15 years old.
"It's such a recent monster," he said. "It only dates back to 1995."
Prior to that, other researchers found a reference to a chupacabra in the 1960s TV show "Bonanza," but it referred to a whippoorwill bird that folklore suggested sucked milk (not blood) from goats, he said.
It wasn't until the summer of 1995, in Puerto Rico, that people started connecting the name "el chupacabra" with the fearsome four-legged creatures thought to prey on other animals.
That's when Madelyne Tolentino, a housewife in the village of Canovanas, reported the first sighting to the local news, Radford said. After years of investigating and tracing the story of the chupacabra backwards, he said he finally reached her through Facebook, via her ex-husband, and interviewed her last year.
Radford said the creature reportedly spotted by Tolentino was about four feet high with oddly-wide, dark eyes, thin arms, three fingers and stood on two legs. She also said it lacked ears, had small air holes instead of a noise and feathery spikes on its back.
"She said she only saw it for a minute or two, it wasn't for very long," he said. "But she gave a whole description of the number of toes, eyes, an alien appearance, the teeth and she even noticed that it had no genitals."
After appearing on the local news, her story was picked up by UFO researchers, who spread the story on the Internet, where it went viral.
"From that point, it leapt from the suburbs of San Juan, Puerto Rico," he said.
When the story aired on "Cristina," a Spanish-language equivalent of Oprah Winfrey's show, he said, it became an even bigger part of the global consciousness.