Gerald Blanchard was a skinny, bespectacled, nerdy kid from Canada who stole millions of dollars from ATMs — and then pulled off one of the most memorable heists in history by parachuting onto the grounds of an Austrian castle to steal the priceless Star of Empress Sisi diamond.

Blanchard, now in his early 50s, is cocky, unrepentant and defiant. He tells his own (oft-exaggerated) story — aided and abetted by interviews with friends and family — in “The Jewel Thief,” a new Hulu documentary directed by Landon Van Soest.

It traces Blanchard’s life of crime in both Canada and the US and ends in a worldwide manhunt spearheaded by two indefatigable Winnipeg detectives.

“Not only is he unrepentant, but as he says [in the documentary] he’s proud of it. He owns it,” Van Soest told The Post. “I see [his life of crime] more as an obsession and an ambition; I think he truly wanted to be great at what he was doing, and he wanted to be recognized for being great at what he was doing.

“So, for him to find an audience, with police willing to chase him around the globe … he feels he’s earned it.”

Born in Winnipeg, and adopted as a baby, Blanchard moved with his single mother to Omaha, Neb.

It was a tough, inner-city environment and he had a tough time fitting in — he was reed-thin, shy and highly intelligent — but emerged from his shell in high school via his newly acquired VHS camera.

Money was tight; Blanchard still blames banks for his family’s precarious finances. In 1987, at the age of 15, he masterminded his first heist, cleaning out a local Radio Shack store, and, put on probation shortly thereafter, he was earning six figures through labyrinthian illegal schemes.

At the age of 16, he bought his first house; nine years later, after a seven-year prison sentence was cut to four years, he was deported back to Canada … and that’s where his story really kicks into high gear.

“I think he has this great ability to revise history to sort of make everything look like he had this great vendetta against banks,” Van Soest said. “What seems very evident is that he had a very deep-seated desire for respect; any entity or person that he felt disrespected him … he spent his whole life trying to prove people wrong.

“He had to show them that he was smarter.”

Blanchard was nearly penniless when he landed in Winnipeg but not for long. He used his electronics genius and painstakingly calculated a way to steal cash from ATMs. His targets included Scotiabank and a brand-new CIBC megabank in which he sauntered off with $750,000 in Canadian dollars — the night before the branch, and its seven filled-to-the-brim ATMs, was scheduled to open for business.

“He certainly sees the world differently than most people,” Van Soest said. “It’s absolutely fascinating … it’s hard to believe that any rational person, certainly someone as intelligent as he is, would attempt these things. But it doesn’t seem to faze him. I don’t know, necessarily, how much of that is bravado.”

Despite his brushes with the law, and time spent behind bars, Blanchard felt indestructible and, in 1998, embarked on his theft of the Star of Empress Sisi at the Schönbrunn Palace in Vienna, which wasn’t discovered until two weeks later (he’d swapped the Köchert Diamond pearl with a replica he bought in a gift shop).

He surrendered in Winnipeg, led cops to the diamond (hidden in his grandmother’s basement) and, in November 2007, was sentenced to eight years in prison. He was paroled after two years.

“It’s this truly kind of fairy-tale-like parachuting into a castle in Austria and stealing crown jewels and this cat-burglar image that’s intriguing to me,” Van Soest said. “What really put [‘The Jewel Thief’] in motion for me was … digging a little deeper and realizing this was not an isolated incident, but decades of an increasing level of ingenuity.

“He’d say to me, ‘Everyone wants to talk about [the palace heist] but I’ve done way more interesting things,’” Van Soest said. “It’s hard to sum up, but so much of it was about finding that recognition, that level of respect.

“He went about it in extremely anti-social and nefarious ways.”