Nick Castle’s side career of being a part-time horror-movie icon comes down to a whim from 40 years ago.

All he really wanted to do was hang out with his old USC film-school classmate, John Carpenter, on the set of his future classic “Halloween” and “demystify the experience" as an aspiring director, Castle says. One rubber mask later, he’s making scary-flick history stalking Jamie Lee Curtis with a large kitchen knife as serial-killing psycho Michael Myers.

But retirement age can’t keep the original Michael down: Castle, now 71, puts on the mask one more time in the new “Halloween” (in theaters Oct. 19). Director David Gordon Green’s sequel, which picks up four decades after Carpenter's original film (and disregards the installments in between), sends Myers on another murder spree through suburbia, though former baby sitter Laurie Strode (Curtis) has been preparing for his return.

While actor/stuntman James Jude Courtney is the main man in the mask now, handling the role's physical rigors, Castle cameos as “The Shape” (how Michael was billed in the 1978 film’s credits) in a crucial scene where Laurie finally sees him again in an upstairs window, on the prowl. She shoots the window out, but it turns out she just saw his reflection in a mirror, which shatters.

“It has all kinds of connotations, I think,” says Castle, who gave Curtis “a big hug” when they saw each other on the South Carolina set. “She said, 'Is this nuts or what?!’ So that was kind of what it felt like: What the hell, this is going on again 40 years later?”

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Castle remembers pretty distinctly “there was absolutely no forethought or preparation” for playing Michael in the original film. “It was John puppeteering me, telling me, ‘Walk here, walk there, tilt your head.’ ”

Carpenter insists there was some reasoning on his part: “The thing about Nick was, his father was a choreographer and Nick has this kind of grace about him. I can't explain it, but he has a unique walk. I asked him because I thought, ‘Well, that would throw us off a little bit in terms of who is this masked man?’ ”

Comparing Castle's Michael to Courtney’s 2018 version, “I was more like a panther and he's more like a lion,” says Castle, who also did a lot of the character’s heavy breathing in post-production for Green's "Halloween." Courtney’s a bigger guy – he’s 6-foot-3, Castle is 5-foot-11 – and “did a really good job. It's a brutal Michael.”

Although Castle misses the old Michael mask (“This one was tighter, so it wasn't as comfortable”), he didn’t have trouble leaving the character behind. Other “Halloween” films followed his first, but Castle instead embarked on a busy directing career that included the 1984 sci-fi cult film “The Last Starfighter,” 1986 family fantasy “The Boy Who Could Fly” and 1996 romantic comedy “Mr. Wrong.”

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Now retired, he spends a lot of time playing with his grandkids (“I have a new generation to bother”) and frequents the horror convention circuit with fellow luminaries like Robert Englund (aka Freddy Krueger) and Linda Blair (Regan from “The Exorcist”).

“I know it will be the thing that'll be my epitaph: They won't say anything about my movies, I'll be this guy in a rubber mask,” Castle quips. “There's the sense that 'Aw, (no), that's gonna be me?' And then there's the other side: I'm a horror icon, so that's not so bad.”