Classic rock has played a prominent role in Showtime’s “Billions,” not just in songs synched on the show — tracks by Led Zeppelin, the Grateful Dead, Sly & the Family Stone, AC/DC and Van Halen can be heard — but in the T-shirts worn by lead character Bobby Axelrod (Damian Lewis) bearing the logos of Metallica, Black Sabbath, Motorhead and other hard rock bands.

The heavy-hitting placements continue this season, the series’ fourth, with songs by U2 (“New Year’s Day”) and Jackson Browne (“These Days”), both used on the most recent May 26 episode. But creators/writers Brian Koppelman and David Levien are quick to point out that the show’s music finds a balance between the familiar and the lesser-known, with such acts as Lucy Darcus, Fred Eaglesmith and Kevin Morby also soundtracking this season.

Indie rock bands like Guadalcanal Diary, The Replacements, Pylon and The Pixies make the “Billions” playlist too — appearances “that speak to our record collections,” says Koppelman, who followed in his father Charles Koppelman’s footsteps by going into the music industry as an A&R executive before turning his attention to film in partnership with Levien. “We are thinking in each episode about the musical palette and finding some unity. Either it’s a thematic unity or it’s a tonal unity in the songs. Or we’re trying to do a juxtaposition to show a couple of radically different emotional states.”

“Billions” is among the premium cable shows that have picked up the mantle from “The Sopranos,” using needle drops to make a significant impact. This season has had two particularly striking episodes musically: One relied on John Mellencamp’s “Troubled Man” and “Bob Dylan’s “World Gone Wrong” to underscore the tortured lives of multiple characters, amplifying the inner-turmoil for each. In another, Joni Mitchell’s “River” was the lone song used, running more than three minutes in the final scenes to underscore multiple sides of “family” and betrayal. In yet another episode, James Brown’s “The Payback” played as if it had been written for the show.

“As we dial in more and more, it’s rare now that if we write a song in and then put it against picture, it doesn’t work,” Levien says.

Friends since childhood, Koppelman and Levien spent much of their formative years sharing an affinity for music and film and taking in many, many concerts. It helped that Koppelman’s father was a music-publishing mogul who scored big on the label side with SBK Records.

“Billions” is the third series the two have worked on together, preceded by “Tilt” and “The Girlfriend Experience.” They also share writing credits on “Ocean’s Thirteen,” Runaway Jury” and “Rounders.” But the Showtime series has proven to be their most music-centric project to date.

“Around the fourth episode, when we found the Andrew Bird song [‘Oh No’], we realized sort of instinctively the way it can function in the show,” Koppelman says. “That episode also featured [multiple] Metallica [songs]. The combination of those things with Eskmo’s score helped us really lock in the tone and voice of the show. … Then it just deepened, as every other part of it does, as we kept making the show.”

Adds Levien: “From the beginning the music was going to drive energy and provide a more energetic counterpoint to the surface trappings of people in offices standing around talking. One approach we take in general is that we try to give the characters credit for knowing everything that we know jointly. That’s the intellectual firepower that they’re working with. They’re hyper-smart with broad points of reference in art and books and certainly in music.”

Since the start, Koppelman and Levien have kept a running list of songs they hope to use; right now it stands at around 120, with more added regularly.

Koppelman declines to discuss budget specifics, preferring to praise Showtime for picking up the licensing tab. Levien sees the process a bit more pragmatically. “There’s sort of a priority list of what are the most important songs versus how much they cost,” Levien explains. “We have managed to include most of the ones that are meaningful. And then in some other spots we’re able to use really unknown types of artists that provide the right backdrop sonically and often lyrically, but for a really low price. Brian has deep relationships with a lot of singer-songwriters and guys in bands that are undiscovered so that helps us get on to them.”