Keep your eye on the quiet ones. See, while it’s the most extroverted musicians who hog the limelight, their unsung bandmates may be creating much of the behind-the-scenes magic. While they might not be songwriters or virtuosos, these folks can be the X factors that hold a band together or help shape its music in less tangible ways. Yet the depth and subtleties of their contribution often are not fully appreciated until they’re gone.

Here are 10 — well, actually 11 — musicians whose impact on their big-selling bands was easy to overlook until they left or were fired (including some who were later welcomed back into the fold).

1. Simon Gallup, The Cure

As The Cure’s only constant member during its 40-year-plus history, singer, guitarist and principal songwriter Robert Smith has sometimes been seen as almost a one-man band. Yet longtime bassist Simon Gallup is deceptively integral to The Cure's sound and success. During Gallup's 1982-84 absence, after a fistfight with Smith, The Cure produced one of its most underwhelming records, The Top (which really was virtually a Smith solo effort), and Gallup soon was brought back. His onstage swagger, skeletal yet indispensable basslines, and under-reported songwriting contribution (keyboard player Roger O’Donnell has stated that Gallup wrote all of the music for The Cure’s biggest U.S. hit, “Lovesong”) have been distinguishing elements of The Cure’s enormous emotional resonance.

2. Izzy Stradlin, Guns N' Roses

It was easy for relatively reclusive guitarist Izzy Stradlin to be overshadowed in Guns N’ Roses, where he was surrounded by larger-than-life characters. But, as well as co-writing some of the band’s best-known songs, Stradlin had an effortless onstage grace, created tastefully song-serving parts, and bonded his often combustible bandmates. “It was Izzy’s fuckin’ band,” former GNR manager Alan Niven wrote in 2014. “He grounded them with his unimpeachable rock & roll stance habitually maintained in his playing and writing. … The cool heart for the hot soul of the band.” Before Stradlin’s 1991 departure (and that of original drummer Steven Adler the previous year), GNR was a gritty, groovin’ band of buddies; afterward, it became an Axl Rose–controlled arena-rock corporation.

3. Glen Matlock, The Sex Pistols

Sneering, spiky-haired bassist Sid Vicious is all but synonymous with not just the Sex Pistols but punk itself. Yet it was his predecessor, Glen Matlock, who actually co-wrote nine of the 11 songs on the Pistols’ sole studio album, 1977’s Never Mind the Bollocks, Here's the Sex Pistols, including enduring anthems “Anarchy in the U.K.,” “Pretty Vacant” and “God Save the Queen.” “He was a good writer but he didn't look like a Sex Pistol,” guitarist Steve Jones told Rhino Magazine in 2005. With Matlock having departed the band prior to its recording, Jones in fact played bass on most of Bollocks, but (with Vicious' death in 1979) Matlock has repeatedly returned for Pistols reunions.

4. Christine McVie, Fleetwood Mac

While the musical and romantic fireworks between Stevie Nicks and Lindsey Buckingham grabbed the headlines, the less flamboyant persona of vocalist/keyboardist Christine McVie belied her equally crucial musical contribution to Fleetwood Mac. McVie had already been in the band for five years when Nicks and Buckingham joined and, even with the duo aboard, continued to be fundamental to its sound. She earned more writing credits than anyone on the Mac’s 40 million–selling 1977 Rumours opus, while her nuanced, bluesy alto lent welcome depth (as lead or co-vocalist) to some of their biggest pop-rock hits. Following a reclusive 15-year semi-retirement in the English countryside, McVie returned to Fleetwood Mac in 2014.

5. The D.O.C., N.W.A

The contribution of Dallas rapper The D.O.C. to genre legends N.W.A was under-recognized even at the time, for the simple reason that he wasn’t actually in the group. Instead, he helped craft the famously incendiary sextet’s sound as a co-writer of classics such as“Straight Outta Compton” as well as eight tracks on their 1991 second (and final) album, Niggaz4Life. After The D.O.C. (and N.W.A rapper/producer Dr. Dre) left Ruthless Records for the fledgling Death Row in ‘91, N.W.A effectively were no more. While he also contributed minor vocals to N.W.A recordings, The D.O.C.’s mic talents were belatedly recognized when his Dre-produced 1989 solo debut, No One Can Do It Better, was certified platinum fully five years after its release.

6. Jamie Stewart, The Cult

Bassist Jamie Stewart is no shredder or songwriter, yet while he was in The Cult — from its roots as Death Cult in 1983 through its mega-selling 1989 Sonic Temple — their career was only in the ascendant. That ended shortly after his final show with the band, at L.A.’s Universal Amphitheatre in April 1990, with stateside sales of ’91’s Ceremony less than a third those of Sonic Temple. Multiple factors influenced this turnaround (including the explosion of grunge) but Stewart, who also played guitar and keys, apparently had a stabilizing influence on the sometimes tempestuous relationship between frontman Ian Astbury and guitarist Billy Duffy. He was invited back for guest appearances with The Cult in 2009 and 2013.

7. Adrian Smith, Iron Maiden

While oft eclipsed by siren-voiced frontman Bruce Dickinson and foot-on-the-monitors bassist/leader Steve Harris, Iron Maiden guitarist Adrian Smith has had a huge impact on the band’s sound during two tenures (1980-90 and 1999-present). As well as forming a formidable twin lead-guitar presence with longtime pal Dave Murray, he was a major contributor to the band’s songwriting, including on hits “2 Minutes to Midnight,” “Can I Play with Madness” and “The Evil That Men Do.” After Smith rejoined the band, Dickinson wrote on IronMaiden.com: “I think everybody was a bit surprised at how much we missed him. … I wouldn’t have rejoined Iron Maiden if he wasn’t in the band.”

8. Mike Starr, Alice in Chains

It’s doubly tragic that much of original Alice in Chains bassist Mike Starr’s more recent fame came from appearances on VH1 reality show Celebrity Rehab With Dr. Drew over the two years prior to his fatal 2011 overdose. He was a supremely stylish player and naturally iconic stage presence whose deeply grooving, proudly functional lines and growly tone deftly underpinned the compositions of Jerry Cantrell and Layne Staley. With bass slung low and hair left long, Starr delivered his parts with a reckless, almost angry attack that was not replicated after his 1993 departure. Nothing personifies Starr’s contribution to AIC better that his ominously hypnotic, subtly detailed bassline for “Would?” which appeared on 1992’s Singles movie soundtrack.

9. Bruce Foxton & Rick Buckler, The Jam

While bassist-vocalist Bruce Foxton contributed occasional songs over The Jam’s six-album spasm of a career, increasingly the band was seen as a vehicle for the prodigious talents of singer, guitarist and principal tunesmith Paul Weller. Sure enough, when Weller went his own way, first with The Style Council (1983-89) and solo ever since, he continued to enjoy commercial success and critical adoration, particularly in his native U.K. But while Weller remains the untouchable Brit Poppa, little of his post-Jam material achieves the taut, grittily nostalgic mod/punk resonance of that trio, suggesting that — in terms of song structures, arrangements and even quality control — Foxton and drummer Rick Buckler were more than just able supporting players after all.

10. Dave Krusen, Pearl Jam

When sales of Pearl Jam’s debut album, Ten, exploded in late 1992 (eventually shifting close to 20 million copies worldwide), it was the dark mane of Dave Abbruzzese flailing behind the drums at their increasingly well-attended performances. But Ten had actually been recorded in early 1991, with little-known drummer Dave Krusen. So it’s Krusen playing on household-name hits “Alive,” “Even Flow” and “Jeremy”. Shortly after Ten’s completion, Krusen checked himself into rehab and out of Pearl Jam, but it was he (alongside current drummer Matt Cameron) who was recognized by the Rock and Roll Hall of Fame when Pearl Jam was inducted last year. “He had something really special,” Pearl Jam vocalist Eddie Vedder told Rolling Stone in 2009.

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