It percolated at the back of his mind until he made a trailer for the nonexistent film as part of "Grindhouse," the throwback B-movie double feature he made with Quentin Tarantino.
That's when the fans, Rodriguez said, practically demanded a "Machete" movie. "People came up to Danny and said, 'You should be doing that as a feature,'" Rodriguez said.
So they decided to make one, for little money and a probable fate on a DVD shelf somewhere. Then some big-name actors such as Robert DeNiro, Don Johnson and Jessica Alba signed on.
"It turned into a much bigger film," Rodriguez said.
At the end of "Machete," Rodriguez threw in a joke reference to a sequel, called "Machete Kills."
"I thought this could easily be a series if we had the wherewithal to make it," he said, adding that he even talked about a third installment, "Machete Kills Again," as a joke.
Again, the fans wanted more. So thus was born "Machete Kills," which expands the Trejo character's range from beyond the U.S./Mexican border to the White House and ultimately into outer space.
" 'Machete' is very much my 'First Blood,' " said Rodriguez, making comparisons to the Sylvester Stallone classic. "He looks like a vagrant, but he's really a highly trained mercenary."
"Machete Kills," Rodriguez said, is more like "Rambo." "It's a much more elevated production," he said. "We wanted to go James Bond with it."
And, like the first film, which co-starred Lindsay Lohan (as a nun!), the sequel features stars with checkered pasts: Charlie Sheen (billed under his given name, Carlos Estevez), Mel Gibson and an armored car designed by car-customizer (and former Mr. Sandra Bullock) Jesse James.
"That's why we call it Troublemaker Studios," Rodriguez joked.
Rodriguez said those stars delighted in playing against type: Sheen played the president, and Gibson is an industrial supervillain plotting to repopulate the planet with an army of super clones.
At one point, when filming with Gibson, Rodriguez rewrote the script on the fly to allow Gibson's character to ride in the Jesse James armored car as an homage to Gibson's star-making role in "The Road Warrior."
"I said, 'Screw the logic,' " Rodriguez said in what could be his motto for making "Machete."
Take, for example, those clones. Rodriguez wrote them in after filming a fight scene between Trejo and Chilean martial-arts master Marko Zaror. "I said, 'I'm gonna find a way in the script to make him clone-able. So Danny can fight him again,' " Rodriguez said.
Rodriguez also populates his cast with some sexy women, including Amber Heard, Sofia Vergara and Lady Gaga. He also gives a featured spot to Alexa Vega, whom Rodriguez has known since she was 11 and starring in the first "Spy Kids" movie. (She's been in all four.)
"I've just grown up with her," Rodriguez said. "She's like my daughter."
But she's also 25 and looking to shake up her onscreen persona.
Vega called Rodriguez, looking for a role different from the "nice-girl kid parts" she was offered by Hollywood producers who only knew her as cute little Carmen Cortez.
"It's the curse of being a Spy Kid you've got too much baggage," Rodriguez said.
Cast as one of Vergara's henchwomen, Rodriguez said, Vega "came full bore and got the most bodacious outfit" essentially a teeny bikini, a pair of chaps and a big gun. A photo of Vega from the set was leaked, and "it changed her image instantly on the Internet," he said. "It was like night and day."
It's not the first time Rodriguez has been responsible for an image makeover. He cast George Clooney, then known only as the nice-guy doctor on "ER," as a cold killer in "From Dusk Till Dawn." And he gave Vega's "Spy Kids" mom, Carla Gugino, a sexy role in "Sin City."
Rodriguez has other projects in the works he's editing "Sin City 2" and launching an action-adventure TV channel called El Rey but the idea of a third "Machete" movie, joked about in a coming-attractions trailer before "Machete Kills," is still out there.
"This is all audience-driven," Rodriguez said. "I thought we were done with the first trailer."
Sean P. Means, for the moment, writes The Cricket in daily blog form at www.sltrib.com/blogs/moviecricket. Follow him on Twitter @moviecricket, or on Facebook at www.facebook.com/seanpmeans. Email him at firstname.lastname@example.org.