It sounded mad, right from the outset. British actor Tom Hiddleston, “Loki” from the “Thor” and “Avengers” movies, as that icon of country music, Hank Williams?

Surely somebody had lost his or her ever-loving mind.

But give it to Hiddleston, who doesn’t lack for that old country music character trait, “chutzpah.” He slimmed down to nothing and took his shot at looking like and sounding like one of the most distinct, keening drawls in music history.

“I Saw the Light” works best if you enter it with those “What were they thinking?” expectations. Because Hiddleston isn’t bad. And if he doesn’t quite nail Hank in his performance of several of the man’s legendary tunes, he puts them over.

And a soulful, “Here’s something I’ve been working on” acapella rendition of “Your Cheatin’ Heart” accompanying himself on guitar, lifts the picture just when you’ve lost hope it ever will be.

“I Saw the Light” takes over two hours to cover the ten years of Hank’s rise and fall, an Alabama singer whose frail health couldn’t take the rigors of the road and the drugs he took just to ease the pain.

See Hank get a reputation as an unreliable boozer, late for shows, missing tour dates. Hear him defend his style of singing to producers who would change him.

“When I find a note I like,” he drawls, “I hang on-ta it!”

Fake black and white “documentary” interviews with music biz folk (Bradley Whitford plays Nashville publisher Fred Rose) who knew Hank pepper the picture, and rather badly mimicked color home movies (and newsreels) chart his rising fame and domestic “bliss.”

That’s the heart of “I Saw the Light,” the womanizing Williams’ combative relationship with his wife and would-be backup singer, Audrey Mae. She battles Hank’s controlling mom (Cherry Jones) for his confidence. And she tries to share the stage with him. Brave as it is of Hiddleston to tackle matching Williams’ unmistakable voice, that’s nothing to what Elizabeth Olsen, as Audrey Mae, has to put over. She has to sing just well enough to have the false confidence of “I could be a star, too,” and just badly enough that she never will be.

Producer turned writer-director Marc Abraham (“Flash of Genius”) struggles to organize this life into a lengthy, neat chronology. And that fails the film. Scene after scene of “red letter dates” in Hank’s story — a “Hank Williams Day” in Montgomery, Alabama, his first night on “The Grand Ole Opry,” an infamous disoriented festival performance in Texas — weigh down the narrative.

Hiddleston can’t pull off the folksiness that was Williams’ public persona. But the better movie this might have been is hinted at in a press interview, later in his life, in New York.

“Ever’body’s got a little darkness in’em,” he allows. “They,” his fans, “hear it. I show it to’em. But THEY don’t have to take it home.”

It’s a fair-minded movie that doesn’t sensationalize Williams’ life or demons. But it lacks heart. There’s no single scene that burns into the memory the way a couple of ones in the corny 1964 George Hamilton bio-pic, “Your Cheatin’ Heart,” do — the wrenching death of the black man that taught Hank to play and gave his sound its earthy, working class soul, for instance.

But Hiddleston comes closer than we ever would have guessed. And when he gets around to “Your Cheatin’ Heart,” you find yourself wishing he’d had a smarter, shorter and brisker film leading up to that moment, a movie worthy of the legend whose story “I Saw the Light” tells.

MPAA Rating:R for some language and brief sexuality/nudity

Cast: Tim Hiddleston, Elizabeth Olsen, Bradley Whitford, Cherry Jones
Credits: Written and directed by Marc Abraham. A Sony Pictures Classic release.

Running time: 2:03