Before joining Metallica in 2003, Robert Trujillo, 52, was as well known for his ability to keep his job under challenging circumstances as for his fast-fingered, R&B-rooted bass playing.

Trujillo toured with Ozzy Osbourne when the Black Sabbath founder was “battling a lot of demons,” and he recorded with Alice in Chains guitarist Jerry Cantrell when the band’s singer, Layne Staley, died of a drug overdose.

“Musicians are interesting characters, man,” Trujillo says. “It’s always important to learn from your life experiences and take that with you into your job situation. You kind of see what people like and what makes them feel good, and how you balance a personality, and you can bring a better vibe to the atmosphere. I call it a gift — I think it is.”

Trujillo joined Metallica at a fragile point in the Los Angeles thrash-metal heroes’ 36-year history. Singer James Hetfield had just returned from rehab for alcoholism; longtime bassist Jason Newsted had recently left the band; and founding members Hetfield, guitarist Kirk Hammett and drummer Lars Ulrich were squabbling so deeply that they attended sessions with a group therapist — all documented in the 2004 movie “Some Kind of Monster.” During that time, the band put out its dark and difficult “St. Anger” album. The film shows Trujillo’s audition, including the band’s reaction: “That’s a ... pretty mighty bass sound you got going there,” Ulrich tells him.

“I try to learn the songs as fast as I can so I can help the others more,” Trujillo says.

With Trujillo’s steady help, Metallica has more than returned to full power — the band is again playing stadiums, and its last two albums, 2008’s “Death Magnetic” and 2016’s “Hardwired ... To Self-Destruct” are old-school, in-and-out thrash metal. Hammett recently told a reporter the band studied its 1983 debut “Kill ’Em All” for “Hardwired” inspiration: “We wanted to return to the idea of short and sweet, fast and loud songs.”

But Trujillo doesn’t totally buy that theory — the album closes with the up-and-down, slow-building, seven-minute “Spit Out the Bone.”

“In terms of the songs being shorter or less arranged, I don’t know that’s the case. A song like ‘Spit Out the Bone’ has a lot of twists and turns. I wouldn’t consider that a song that’s less progressive,” he says.

Veteran fans know Metallica maintains a swing underneath those brutal guitar riffs, a quality Trujillo connected with immediately. “I’ve always felt Metallica has a groovy ingredient. There’s a funkiness to the music even if you go back to songs like ‘Disposable Heroes’ or ‘Sad But True,’?” Trujillo says. “No matter how heavy it is, you’ve got to have your foot stomp to it — or head-bang.”

Steve Knopper is a freelance writer.