The Eagles?

His movie career took him away from music for a long time...

Simon & Garfunkel? ('81)

....Pinky and Perky?

one or more of the US soul/R&B/Doo Wop bands like the Platters, The Drifters and The Coasters.

These bands are still doing endless tours with varying numbers of orginal members (sometimes with NO original members, in fact), but this has been going on since the mid-late 60s.

I dare say the big jazz bands like Glenn Miller (without Glenn, of course) were doing it even earlier.

In rock Traffic got back together in 1970 for the John Barleycorn album after Winwood had swanned off with Blind Faith and Airforce for a year or two.

...that we could go even further back than the Glenn Miller band (who, to be fair, didn't exactly make a comeback - they just carried on without Glenn for obvious reasons. Unless I'm wrong and there was a gap between Glenn's disappearnce [NOT a cue for the conspiracies people to jump in!] and the band continuing?).

Surely there were 'original' dixieland bands from the very earliest days of recording, or indeed pre-recording, who became legendary during the trad jazz boom in the 50s and reformed? Very hazy on that point, but I have dim recollections about reading stuff to that effect at some point...

But getting back to Traffic et al - you're right in that it seemed to be the case that a number of big name acts in the late 60s/early 70s split, members did other stuff for literally a couple of years - and in those days, when things seemed to move quicker, that might mean form/tour with two or three bands and make several records - and then the original act reformed, with it being billed as such (maybe with a new member or so added). I can think offhand of both Free and Mountain - the latter splitting in 1972 and reuniting in '74; Free, from memory, split in 1971 and reformed in '74 (though I might be out a year or two on that one).

But in terms of what we might think of as being a reunion of a big act from the time of one generation in the time, more or less, of another then I think Simon & Garf (as mentioned above) reuniting in 1981 after 11 years must be the start of the big modern reunion events.

that the original line up of the Ma Sive string quartet who were very popular among the North London intelligentsia became a three when Ellen Marks (cellist) left to join the Mo Jo tea dance band. Obviously following the great victoria sponge incident in 1910 (let's not go there again) Ellen was welcomed back into the fold by the remaining 3 who had muddled on to dwindling audiences who couldn't accept them without Ellens legs spread wide around her instrument Dame Hep Worth, Lew Ry and violinist Moss Man reformed in 1911 to take pre-war London by storm. As we know their tragic end while playing Colonel Bogey to the troops to raise their spirits during the battle of The Somme is well documented and needs no repetition here. Except to say they never did find their bows.

As a kid I recall the original line-up of The Animals reforming in 1983 for an over-hyped yet less than successful regrouping - BBC's Nationwide even did a mini-documentary on this at the time.
( The failed '83 Animals reunion featuring a reformed band who'd forgotten that they'd originally split because they hated each other's guts was also the inspiration for Likely Lads writers Dick Clement and Ian Le Frenais to pen the movie Still Crazy )

However Wikipedia says the original line-up also reformed in both '68 and '75 for gigs and recordings, which must be some kind of record if it's true

.

also re-formed in 1975 with Rick Wills in place of Ronnie Lane.

They toured and recorded an album, but it was all a bit half-arsed.

(technically not the name of a band but anyway) I recall must have been the person first responsible for saying 'right, that's it, I've had enough' and then re-appearing, gig-wise, six months later. And I'm sure the Who and the Quo, during the 80's, were guilty of many 'comeback' tours.

"Hell Freezes Over" tour & album was certainly the first tour deliberately marketed and promoted as a "heritage" event.

...been retired for about 30 years when he was rediscovered in the '60s?

...what has been the longest time between original band and reformation.

I believe the Incredible String Band have the record of longest gap between John Peel sessions (related to their reunion): 10/73 to 11/2000.

But I imagine the Pe****gle might have had a decent claim on the longest gap - 3/73 till 2007. Except that's scuppered by a brief reunion to tour Italy & Australia in 1983...

What about Van Der Graaf Generator - c1975 till about 5 years ago, wasn't it?

The Ink Spots were the first band that came to my mind and I started picking through the account of their various line ups in wikipedia but lost interest. Blimey. What a fractured history.

http://en.wikipedia.org/wiki/The_Ink_Spots