Before there was Superman there was Joe Greenstein.

And if you think the story of an infant rocketing to earth from an exploding planet, raised by a small-town farmer and his wife, fighting for truth and justice and the American way, is hard to believe, well, to quote Al Jolson, you ain’t seen nothing yet.

Greenstein’s life is told in an engaging documentary called “The Mighty Atom,” the nickname earned by the 5’4,” 140-pound very unlikely strongman.

It may not be much of a reach to suggest (as the filmmaker does) that because Superman’s creators, Jerry Siegel and Joe Schuster, were Jewish, “maybe they knew” about Joe’s feats. It probably is going a bit overboard to imply that they patterned the Man of Steel after the diminutive strongman who bit through steel. But then again, the filmmaker, Steve Greenstein, is Joe’s grandson.

For the record, that’s not a misprint. Joe’s strongman feats included biting through a chain, bending horseshoes and pulling cars and trucks using ropes attached to his hair or in his mouth.

Joe Greenstein pulled cars with a chain in his teeth.

Greenstein was born in Suvalk, Poland, in 1893. He was sickly when he was young, suffered a variety of respiratory ailments, and was diagnosed with consumption — that’s what they called tuberculosis then — when he was 14. He was given four, maybe five years to live.

Sneaking into a traveling circus, he met the show’s strongman, a Russian who went by the name Champion Volanko. Volanko, who was Jewish, felt sorry for Greenstein and took him under his wing. Greenstein joined the circus, and using Volanko’s training regimen (as well as dietary and breathing techniques he supposedly picked up in his travels through Asia) apparently was able to prove the doctors’ diagnosis wrong.

After about 18 months on the road, he returned to Poland, got married, and started a family, but because of ever-present anti-Semitism, emigrated to the United States, landing in Galveston, Texas.

He opened a gas station. That’s where, according to legend (and Steve Greenstein), fate intruded. Harry Houdini was one of the passengers in a car that had a flat near Joe’s station. Greenstein changed the tire without benefit of a jack. He simply lifted the car with one hand and put the tire on with the other.

The group’s manager was so impressed, he signed Greenstein as a client and booked him on tour as — wait for it — the Mighty Atom. That’s because the thing that made Joe unique beyond his strength was how small he was.

As Edward Meyer, a Ripley’s Entertainment executive, notes in the film, in the world’s strongest man competitions, typically the contestants all are around 350, maybe even 400 pounds. “A small guy is always going to steal the show,” he said.

Steve Greenstein, Joe’s grandson

Greenstein was also unique because, as a few people stereotypically note, Jews are not a people known for physical strength.

Even before the IDF, Greenstein proved that conventional wisdom wrong. The film recounts an episode where Greenstein came across a Bund meeting sign that read “No Dogs or Jews Allowed.” He ripped it down, and when the attendees came out to challenge him, he took them all on with a bat. A Hank Greenberg bat.

Greenstein’s specialties, in addition to bending metal, were pulling heavy objects (cars, trains) with his teeth and banging a nail into wood using just his hand. He even stopped a small plane with his hair.

He used his various platforms — the vaudeville stage, county fairs — to preach the benefits of a healthy diet and exercise. Oh, and also a line of elixirs he developed.

Joe continued to entertain until just a few months before he died in 1977. He often appeared with his sons, who seemed to have inherited his strength gene. His son Mike was 93 when he appeared on America’s Got Talent in 2014 and pulled a 3,500 pound car with his teeth.

The Mighty Atom is harmless fun. It wanders a bit and the viewer never is completely sure what is fact and what is hyperbole. But true or not, it’s nice to think we had our own Superman.