Michael Nesmith of the Monkees. Incredibly talented, and I get to inherit a fortune!
Tony Banks of Genesis.
Phil Collins and Peter Gabriel are obviously very well know. Mike Rutherford had a number 1 hit with his “side band” Mike + the Mechanics. Steve Hackett is still selling out shows across Europe. Tony Banks has never had any success with his solo stuff, and has never said a word on stage in 40 years…but he’s the man who defines Genesis’ sound.
John Deacon of Queen.
The others all sang, the others all took star turns. He just played bass and lived quietly.
On Queen’s Greatest Flix, their collection of videos from the 80s, the all listed their favorite drinks. The other three gave cocktails or somesuch. Deacon just said, ‘tea’.
I caught an interview with Roger Taylor a long time ago in which he was asked, ‘What’s John doing these days?’ His reply? “Not much.”
Played in a band. Made a lot of money. Band ended. Went home and stayed there being rich.
Gotta admire that.
Meg White.
I can’t sing at all, so I’d love to have the voice of young Art Garfunkel.
Bootsy Collins or Bernie Worell since JPJ and Michael Anthony were taken (among others). Jim Messina had a good thing going on.
I don’t know how she compares, but my sister plays like that. She is an Oberlin graduate and toured Europe for awhile. She has a church organ in her home that we rescued from an old church being remodeled. 16" Leslie speakers! I tried very hard to rattle proof the house wile she played the low notes. But everything that can move: windows, doors, cabinets, etc, just vibrates like heck.
Anyway, she wears ballet slippers to play.
Dennis
John Entwhistle.
Sure, who wouldn’t.
I kinda get the impression, though, there is (or at least was) some underlying bitterness on his part about being the Other Guy.
Apparently, she would disagree with you. To my knowledge, she stepped away from the White Stripes because she had issues with anxiety. She obviously wasn’t a trained drummer and basically just keyed off Jack’s playing - the amount of derision she got must have been very hard to deal with over time. I thought she was great.
This. Or Roy Bittan of the E-Street Band. Or Benmont Tench of The Heartbreakers. Or Garth Hudson of The Band. There’s no lack of great keyboard players who are vital to their outfits while maintaining a low presence on/offstage.
As a keyboardist, or sometimes keyboardist, or whatever you wanna call me, Tony Banks is absolutely one of my favorites. Good call. I thought about it in this thread, but didn’t think he qualified as “the other guy” since he was so instrumental in the sound and I thought perhaps more well known than he actually is. But if he does, another vote from me.
Or a Pip.
Yes! 
HA!
Phil Volk, aka Fang, from Paul Revere and the Raiders. He was cool as hell, was better looking than either Paul Revere or Mark Lindsay, and has been married to his hot wife for almost 50 years.
Yeah, I watched Under Northern Lights the other night, and it seems like while Jack thrived on the attention, she have rather been doing anything else than touring and fronting to the public. I hope she found happiness away from the limelight, but I miss her drumming.
Martin Barre
Took over for some guy named Tony Iommi in 1969 as the lead guitarist for Jethro Tull, and is the only band member to stay with Ian Anderson until the band went defunct in 2014.
Bob Daisley.
He was in:
Mundgo Jerry of “In the Summertime” fame
Widowmaker
Rainbow
Ozzy
Uriah Heep
Gary Moore
Black Sabbath
Living Loud
He also played on a bunch of other albums as a guest or session player. Daisley has been the other guy in a bunch of extremely successful bands and wrote a ton of stuff.
Slee
The first name that came to mind is Dave Mustaine. Not only did he avoid becoming a sad footnote in music history, he went out and started a band essentially as important as the one that threw him out. No easy feat!