Nearly 40 years after a B-side track from McCallum’s sophomore album — an instrumental record consisting mostly of pop covers — dance and hip-hop DJs began sampling the moody, slinking track, “The Edge.” Its most famous appearance came in 1999, when Dr. Dre cued up the twangy, 12-note pattern at the start of the song for the intro of “The Next Episode.”

Decades before McCallum starred as the “NCIS” fan favorite “Ducky,” he was a 31-year-old blonde heartthrob, building an acting career after his musical aspirations had been curtailed by a conscription to the British military.

Eager to capitalize on McCallum’s mid-60s star power, Capitol Records teamed him up with in-house producer David Axelrod and banked on a hit.

“It was entirely money making on behalf of the studio,” McCallum told the Scottish Daily Record in 2018. “ ‘Man From U.N.C.L.E’ was a hit. I was popular so they said, ‘You have to sing on an album because it will sell lots of records and we’ll make money.’ I said, ‘I don’t really sing.’ I was a musician.”

McCallum’s instrumental record “Music … A Part Of Me,” debuted in February of 1966 and spent eight weeks on the Billboard Top 40. His follow-up record, “Music … A Bit More Of Me,” was full of instrumental covers of popular songs like Stevie Wonder’s “Uptight (Everything’s Alright),” the Beatles’ “Michelle” and the “Batman” TV theme.

The album’s liner notes give passing reference to “The Edge,” the record’s 2:49-minute penultimate track inspired by the poverty Axelrod saw on a tour of Puerto Rican shantytowns and written specifically for McCallum.

“Music … A Bit More Of Me” and McCallum’s follow-ups were successful records (though modest chart hits). McCallum reportedly drew more fan mail than Elvis at Capitol Records at the time, largely because of his “Man From U.N.C.L.E.” fans.

“I just did what they wanted. I wrote the orchestrations, conducted the band, made the recordings and had a wonderful time,” McCallum said in the 2018 Daily Record interview.

Though McCallum’s fame drove fans to his records, Axelrod is known as the musical genius behind the hits. Axelrod, who died in 2017, was known for his influence on hip-hop, a legacy that the Guardian, in a 2017 tribute, credited to his “richly cinematic and mysteriously evocative” work, which “could bring whole new dimensions to a track.” Prominent artists such as Wu-Tang Clan, Lil Wayne and Eminem all dipped into Axelrod’s oeuvre at one point. And in 2004, Axelrod said that the royalties from “The Next Episode” allowed him to pay for a 26-piece orchestra for a performance.

McCallum’s musical career, meanwhile, had been eclipsed by his acting roles by the time Dr. Dre sampled the 12-note pattern for “The Next Episode,” swapping trumpets and flutes on “The Edge” for Snoop Dogg’s unmistakable “La dah dah dah dah.” The energetic hip-hop hit went on to earn a Grammy nomination in 2001 and went double platinum in the U.K. Last year, Dr. Dre and Snoop Dogg opened their historic Super Bowl Performance with the song.

(Dr. Dre, notably, wasn’t the first or the last to sample “The Edge,” with acts such as Scaramanga and Missin’ Linx utilizing snippets of the song before Dre, and John Legend and Kendrick Lamar following years later).

McCallum, who was 66 when his track was sampled, earned a credit on Dr. Dre’s album — one of many creative achievements, according to his family.

“He was a true Renaissance man — he was fascinated by science and culture and would turn those passions into knowledge,” McCallum’s son, Peter, said in a statement following his father’s death. “He was capable of conducting a symphony orchestra and (if needed) could actually perform an autopsy, based on his decades-long studies for his role on NCIS,” he said.

In addition to TV and movie stardom, McCallum appeared in theater, wrote a novel, and could carry a beat, too.