For decades, he’s been a “Hey, it’s that guy” guy. The goofy newspaper editor in the “Spider-Man” movies. Juno’s dad. The neo-Nazi on “Oz,” the recurring police psychiatrist on three of the “Law & Order” shows.

And those were the glamour roles. When no one else wanted him, he was the yellow M&M on the candy commercials. He continues to do hokey Farmers Insurance ads.

Now, just turned 60, it turns out That Guy has a name, one that may be soon attached to a Golden Globe and then to an Oscar: Jonathan Kimble “J.K.” Simmons, consummate character actor and team player, who stepped forward and lit the screen on fire this year as the brutal, contemptuous, unforgettable music teacher Terence Fletcher in “Whiplash,” one of the year’s most acclaimed dramas.

In showbiz, of course, Simmons was already a name because backgrounders like him are essential to the machinery: “I’ve heard people say a ‘J.K. Simmons type, but younger’ or ‘J.K. Simmons, but with hair” or ‘J.K. Simmons but Mongolian,’” the actor told Interview. “The next step is for a ‘J.K. Simmons-type…Oh, you mean he’s still alive?’”

“Whiplash” writer-director Damien Chazelle pitched Simmons the role unaware that the actor had a deep background in music. A singer (he has even performed Wagner), Simmons has a music degree (in voice) from the University of Montana, where he minored in composing and conducting.

He and Miles Teller, who plays the young drummer Fletcher browbeats toward greatness, were equally dedicated to their grueling parts.

Well, more or less.

“He was reluctant to be slapped really hard dozens of times, and I couldn’t understand why he wouldn’t enjoy that, that level of acting and commitment,” Simmons told Rolling Stone.

To NPR, Simmons conceded that though the role of a borderline psychotic perfectionist was cathartic, “screaming is hard after awhile.”

What’s most electric about the film is that Simmons is so charismatic — sarcastic, funny, alert, wise, dedicated — in portraying Fletcher’s cruelty that until the final moments we’re never quite sure whether he’s the villain or the hero: whether he is rescuing the drummer from a life of mediocrity or destroying the younger man’s self-esteem.

“Really the nature of the story is, does the end justify the means?” Simmons said. “How far is too far? How much can you push people in the name of artistic greatness without sort of sacrificing humanity?”