Ringo Starr was in Rory Storm and the Hurricanes, which was a well known and successful band around Liverpool. Then he left them to join the already-established Beatles.
Matt Cameron was the drummer for Soundgarden until he was the drummer for Pearl Jam.
How about Terry Williams? He played with Dave Edmunds in Love Sculpture then went on to play with Man, Rockpile and Dire Straits.
Don “Sugarcane” Harris. Was a member of the west coast band Don and Dewey, and later joined the Mothers of Invention and John Mayall’s Bluesbreakers.
Timothy B. Schmidt. Started out with Poco, then joined the Eagles. Post-Eagles, he joined Jimmy Buffet’s Coral Reefer Band.
Buckethead was an established solo artist and member of praxis before joining guns n roses.
Drummer Marc Bell started in Richard Hell and the Voidoids before changing his stage name to Marky Ramone and replacing Tommy in The Ramones. He later drummed for an early-2000s Danzig-less version of The Misfits
Heavy Metal and Heavy Rock musicians are always moving around.
Ian Gillan became famous with Deep Purple. Had success with Ian Gillan Band and Gillan. Then joined Black Sabbath for a single (not hugely successful) album.
Michael Schenker found fame with the Scorpions. Had success with UFO. Had further success with The Michael Schenker Group.
A non-metal example. **Neil Finn **became famous after joining New Zealand band Split Enz. Became even more famous with his own band Crowded House. Had a successful solo career as Neil Finn. Has now joined Fleetwood Mac.
TCMF-2L
Aynsley Dunbar started out with John Mayall. He later joined Frank Zappa, Whitesnake, and UFO. Of course he was also an original member of Journey.
I’m seeing a certain prejudice in the OP, here. Yes, there are ‘name’ musicians who’ve done this. But the winner will almost certainly be someone hard to track down as session musicians end up playing with many bands over time…some of them for quite a while. A lot of it will depend on your definition of ‘known’.
Does The Wrecking Crew count? They were sure known at the time and ended up playing on - essentially joining for studio work - with The Crystals, The Beach Boys, The Byrds, The Mamas and the Papas and a ton of others. Some of the guys in there have music credits for more than a hundred top 40 records.
Or the horn guys from Muscle Shoals? Or the astonishing players Barry Gordy put together as the Motown band? Many of them joined various bands through the studio system and were very well known at the time.
Hell, look at Bootsy Collins, one of the best bass players ever. Came up through The Pacemakers but eventually joined James Brown’s band and then went on to join Funkadelic and later Parliament (it gets complicated from there). But in the end he was essentially a great musician who got invited to play with a lot of people.
But also on your definition of “joined.” A session musician may play with many bands without being an official member of any of them.
Session musicians wouldn’t meet the criteria set out in the OP because they were never part of the band. For many bands I don’t know if there’s a true definition of “band member” although I suspect it’s centered around money/contracts.
Actually, lots of the people suggested in the thread don’t meet that criteria since they founded one the bands mentioned.
A case that I don’t think counts, but that illustrates how specific the requirements are: Todd Rundgren.
He joined (some of) The Cars for awhile to become The New Cars, and he joined Ringo Starr & His All-Starr Band. But it’s debatable whether the former counts as an established group or a new one, and the latter is disqualified as being a “supergroup.” Todd was also in The Nazz and Utopia, but those were bands he formed, not bands he joined.
Indeed. And that’ll send us down a real definitional path. What about Joey Waronker? He was Beck’s drummer and played with REM for four or five years when Bill Berry retired but was never an actual ‘member’ of the band. Still, touring for years with them and recording a few albums with them? Does that make him a member even though for dollar reasons he wasn’t a member?
Yes, well, I was afraid this thread would start to break down, because “established” is hard to define, and there is a lot of gray area. I did have “being an official member of a band” in mind when I wrote the OP. But then again, being a member of a solo artist’s band may not legally be defined as “official member,” so… more gray area!
Let’s not worry about a precise definition so much, and just see where this goes. The only thing I’m really trying to avoid is musicians who started their own bands, or took part in forming a supergroup.
Of the artists listed so far, the winner seems to be Aynsley Dunbar, who has joined up with a lot of already-known artists and bands.
Nitpick – Prairie Prince (The Tubes) was Journey’s original drummer.
EDIT: Well, Prince’s tenure as Journey drummer was very brief … like maybe a month.
EDIT 2: Prairie Prince was the drummer for while of the proto-Journey backup band put together by Santana’s manager. It gets kind of complicated the more I look into this 
My first thought was Ringo Starr. His success with Rory Storm and the Hurricanes lead to replacing Pete Best in The Beatles.
I’m mystified as to why anyone would think Ringo qualified.
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Rory Storm was a local Liverpool band that didn’t have a recording contract. There are hundreds of rock musicians who played in bands that never made it before joining the group that led to their first success.
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The Beatles were hardly “established.” They hadn’t even recorded an album. They were just a good local group with a new recording contract.
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After the Beatles, Ringo fronted his own bands, all of which were new and not established.
My first thought was Ringo Starr. I didn’t say it was a good thought?
How about Nils Lofgren? From Neil Young’s Crazy Horse to replacing Steve Van Zandt in Springsteen’s E Street Band?
I’ll note that the OP specified that he was looking for examples of musicians who had already established themselves in some fashion (for whatever that might mean), and who then joined more than one already-established band (i.e., probably replacing someone else each time).
I note this mostly because a number of the suggestions that have been made don’t fit the criteria – either the guy only joined one already-established band, or he became part of a new group from the start.