Scott C Waring has spent the last seven years reporting alleged UFO sightings every 24 hours on his website ufosightingsdaily.com.
It had grown to become one of the most well-known UFO websites in the world, with its reports regularly followed up by media across the globe.
Mr Waring also published the results of his own “research” on the website, which involved spending hours looking through images placed online by NASA of the Martian surface looking for signs of alien life.
The conspiracist produced several reports claiming to have found creatures which resembled animal species on Earth, including a giant mouse, baboons, a bear, and crabs.
He also claimed to have found fossils and skeletal remains of an ancient humanoid civilisation he claimed once inhabited the Red Planet.
But Mr Waring, who had posted each day this month, suddenly stopped on Friday, releasing his final post.
He wrote: “My last post. Thanks for the seven years of support. We have accomplished a lot together.”
He said he started the blog as a place to defend UFO witnesses, who often faced ridicule.
“Now that happens less,” he added.
He said that pressure from readers of his website had pressured NASA into axing a decision to stop a live feed camera on the International Space Station – which was another source on many of the UFO sightings on the website.
He said: “The cams are still up, years later.
“We posted some amazing sightings and discoveries along those seven years and we have made it to major news sites like CNN, NBC, ABC, CBS, Fox News and even New Scientist which said I was making a new area of science.”
But after saying ridicule against UFO hunters was less frequent now, he appeared to blame it for his own decision to quit.
He said: “I think it’s changed. It was educational before, it was enlightening before, it was even comforting somehow knowing the truth, but it seems to have taken a turn as entertainment.
“That was never my intention. This is serious stuff that has depths that even I can’t fathom. It deservers serious thought and research, not contempt and ridicule.”
His departure has had mixed reviews among other UFO buffs.
Nigel Watson, author of the UFO Investigations Manual, told Express.co.uk: “I think he was genuinely trying to find and share UFO sightings and anomalies captured by the cameras of the International Space Station and other space vehicles, but the sheer quantity of his ‘discoveries’ undermined their quality.
“This has led to criticism and inevitably ridicule, and the sad fact is that the subject relies on sensation and entertainment rather than searching for genuine evidence or data.
“I think Scott, like many others who become involved with the UFO subject, got obsessed with seeing evidence of UFOs and aliens everywhere.
“How many people really believe his photographic evidence that everything from massive skyscrapers to squirrels exist on the surface of Mars.
“Ninety-nine percent of his site was wishful thinking, yet you can’t help but be amazed by his imagination and enthusiasm.”
Scott Brando, who runs the hoax-busting website ufoofinterest.org was pleased to see Mr Waring stop.
But, even he said there was an air of mystery about the sudden decision.
He said: “Perhaps he has made a serious mistake and must disappear for a while?
“Or perhaps it’s just a break or to test the reactions of his followers.
“But if this statement is true, the UFO Community will be better without him.”