In 1950s Hollywood, the most popular pictures were lavish Technicolor epics set in ancient Greece or gladiatorial Rome.  Howard Hughes’ “The Conqueror” with John Wayne as the mighty Mongol Genghis Khan stands out among these – as being unbelievably terrible.

It’s awful enough for “Conqueror” to be included in “The Fifty Worst Films of All Time” book. It’s also now notorious, as William Nunez explains in his fascinating documentary “The Conqueror: Hollywood Fallout.”

In 1955 “The Conqueror” filmed in the expansive mountains of St. George, Utah, with America’s most popular star mightily miscast opposite fiery redhead Susan Hayward, also seriously miscast as a Tatar princess. Dick Powell, a ‘30s musical star turned hardboiled ‘40s hero, directed, reportedly for the sizable paycheck from billionaire producer Hughes.

While “Conqueror” has inspired much mockery for its sheer ridiculousness, it was a box-office hit around the world.

What everyone failed to realize as they spent months filming, was they were directly downwind of military atomic bomb testing.  Decades later, it was revealed the government knew what radioactivity would do — but warned no one.

The radioactive fallout is credited with creating a cancerous “Conqueror” plague: Wayne, Hayward, Powell and co-stars Agnes Moorhead (“Bewitched”) and Pedro Armendáriz (“From Russia With Love”) all had early cancer-related deaths.

It was calculated that of 220 cast and crew, there were 91 cancer victims with 46 fatalities. The film chronicles not just the celebrated victims but the many locals as well. Residents often saw their children be the first to die as the town’s losses continued.

Nunez’s research began with the stars’ children. “Patrick Wayne’s in it. Tim Barker, Susan Hayward’s son, is in it. They had, obviously, brothers and sisters and all that but I specifically picked Patrick and Tim because they were actually there on location,” he said in a phone interview.

“I did reach out to Dick Powell’s son, did a pre-interview with him — a snippet’s in the documentary — but unfortunately, he passed away before production.

“That’s the amazing thing. That was another rush, to try and get these stories now because since then, two others have passed away.”

We see testimonies from women, survivors of thyroid cancers who’ve lost family members.  “As the film shows,” Nunez said, “radiation just doesn’t stop in St George. It’s spread throughout all of North America.”

“The Conqueror: Hollywood Fallout” is available on VOD