In Hollywood, they call it “on the nose” casting. And if ever you doubted that Matthew McConaugheywas the perfect pick to play the yarn-and-myth spinning rural romantic title character in Jeff Nichols’ Southern Gothic melodrama, “Mud,” he puts your mind at ease the way Mud himself would — with a tale.

Mud, a good ol’boy on the lam and on the lookout for his life’s true love (Reese Witherspoon), may be Nichols’ (“Take Shelter,” “Shotgun Stories”) invention. But he is the laid-back Texan McConaughey’screation. Mud is a rough-hewn romantic, someone the well-traveled McConaughey has crossed paths with in the trailer parks and marinas where drifters and cruisers wear the label “off the grid” as a badge of honor.

“I met this sailor down in the Caribbean about ten years ago,” says McConaughey, who has done his time in trailers and boats. The guy was a round-the-world cruiser, and an unforgettable character.McConaughey summons up the sailor’s voice to tell his story, a guy who sounds, on every level, an awful lot like Mud, who also lives on a boat.

“‘I was workin’ offshore, off Florida there for a while,'” McConaughey says, affecting a non-Texas drawl. “We’d come ashore on the weekends, and we’d hit this dance club. And there was this one girl workin’ there, and I took one look at her and said, ‘Oh my GOD.’ I was in love, straight off. She wouldn’t talk to me or nothin’, I’d tip her and tip her. I kept asking her to come to lunch with me on my boat. She said ‘No’ five times. But the sixth time, I got her to come meet me on my boat for lunch. Soon as I got her on my boat, we took off –kept going, all the way around the world.'”

McConaughey laughs at the outlaw nature of that, the chutzpah.

“So he took this lady on board his boat, first date and all,  and basically kidnapped her. She didn’t talk to him for two months! But they got married in Spain, finished their round the world voyage, and had a beautiful daughter.

“That guy is somebody, like Mud, willing to show you how far he’d go to win a woman. I don’t necessarily approve of what he did, but I love the spirit of it. He inspired me when I thought about how to play Mud, the place Mud was coming from.”

Mud, who meets and recruits two Arkansas river rat teens to help him in his quest, is a character cut from Southern myth, a Huck Finn or Harry Powell, the Robert Mitchum menace from the classic “Night of the Hunter.” Variety’s Peter Debruge describes him as “feral,” a waterfront philosopher/outlaw who benefits “greatly from that itchy unpredictability only McConaughey can bring.”

“He is superstition and memory and a guy I could grab ahold of and say, ‘I get him,'” MConaugheysays. “How far towards the ends of the Earth, to limits of the universe would a man go to be with the woman he has decided is his one, true love?”

McConaughey, 43, has had a run of guys he can “grab ahold of.” Starting with “The Lincoln Lawyer,” the hunky leading man, long dismissed for gracing middling romantic comedies and muddled thrillers, has been on a roll — “Tropic Thunder”, “Killer Joe”, “Magic Mike” and now “Mud” — compelling performances, often in supporting roles and always in good movies. The streak led New York Times critic Manohla Dargis to wonder “What happened? Did he roll out of bed one morning” with his movie-choice mojo back in hand?

“I think I’m making, actually, more selfish choices these days,” he says, on his way to the set of a cable series with the working title, “True Detectives” that he’s doing with Woody Harrelson. “These roles are all challenging me, scaring me. I like that. ‘I’m not sure how to play that. I’m not sure how to solve that acting moment that’s in the script. I don’t know how this guy works.’ And that’s a real turn on.”

He dragged his family to Arkansas for the two month “Mud” shoot and gave them as much of an authentic outdoors, off-the-grid experience as he could. A guy who traveled the country towing a trailer, on occasion, a man who knows his way around “live-aboards,” those who live a gypsy life on board cruising trawlers or sailboats, he sounds a little wistful that the character he played lives in a way he could never live again.

“You go in any marina, you find people like this. You don’t uproot your life and dive into that lifestyle without some need to lose contact, to check out. There are a lot of wonderful vagabonds, pirates and outlaws that live like that, off the grid and on a boat.

“People don’t hop up and offer their full name right away when you meet’em. They hold back. It’s ‘Hey, man.’ They don’t call each other by their first names, maybe they’re not even living under their real name.

“Boat living is similar to trailer living. It’s rootless, immediate. You want to leave, you hook up and pull out. You’re gone. No need to go and tell anyone, ‘Hey, I’m leavin’. No need to say ‘Goodbye,’ nothing. Your neighbors wake up in the morning, and you’re gone.”

There’s a faintly rueful laugh. An A-list actor on a roll, a married father of three has little chance of going back to anything like that lifestyle himself. But actors live vicariously through their roles. And “this guy Mud, what a FUN guy to run into. A real character, a dangerous guy, possibly. But a pure-hearted soul who’s out there living a boy’s dream — on an island, on a boat. Two boys helping a man on the run and in love.

That’s a summer adventure like Mark Twain would have dreamt of.”