One of most-forgotten of those great strips is Elzie Crisler Segar's Thimble Theatre: usually called by the name of its most famous character, Popeye, and overshadowed by his later exploits in bigger media (the Fleischer cartoons of the '30s, the many TV cartoons since then, the odd Altman live-action movie from 1980), Segar's original is a full-bodied funny adventure strip, with long, intricate continuities and a large cast of quirky characters. (Though Popeye was clearly the central character from soon after his introduction.) Fantagraphics has been reprinting the Segar Thimble Theater run, from Popeye's introduction in 1929 (ten year's into Thimble Theater's run, actually) through Segar's death in 1938, with four volumes out so far and a fifth due to be published within a couple of months. (I saw the first book back in 2008, and was very impressed -- impressed enough to get volumes 2-4, actually, though it's taken a while to work out a time and place to actually read these impressively large slabs of comics.)
The second book is Popeye: "Well, Blow Me Down!" -- the actual volume number is buried in the copyright information on the title page ; each book does stand alone, though, since each reprints whole continuities -- which was published in 2007 and reprints daily strips from December, 1930 through June 1932 and Sunday strips (which had a separate continuity) from '31 through October of '32. It also has a very short foreword by Mort Walker and the first half of a only mildly tedious academic-style article by Donald Phelps. 
Those who are used to only the post-Fleischer Popeye plots -- a large beefy type named either Bluto or Brutus kidnaps Olive; Popeye's strength is insufficient until he gags down a can-load of spinach; Popeye clobbers the man named B and embraces Olive -- will be surprised to see how expansive and inventive are the stories here. The dailies, with a broader canvas and longer continuities, first send Popeye and Olive's brother Castor out west to capture the notorious outlaw Glint Gore, then back for Popeye to spend his reward money setting up a "one-way bank," and then off to the South Seas for a long string of stories about the war between the nations of Nazilia and Tonsylvania, before ending up with another western story, with Popeye trying to clean up Skullyville, "the toughest town in the world." And those daily strips are a generous six panels long, giving Segar lots of space for wordplay, fighting, and various shenanigans.
The Sundays are somewhat more domestic, sticking closer to home, mostly with stories about Popeye's boxing career (taking on a series of bruisers set up by Mr. Kilph, who hates Popeye for reasons explained in the first volume), and many, many cartoons about Popeye calling on Olive or hanging out at restaurant run by his friend Rough-House. Along the way, a boxing referee named Wimpy shows up, and begins sticking around, continually bugging Rough-House for a hamburger (to be paid for on Tuesday, naturally) and, at the least sign of impending violence, declaring "Let's you and him fight." (Though that sentence is one a boxing referee could use a lot in his working life, and Wimpy does.)
Also included on the Sunday pages are Segar's contemporaneous Sappo strips, about a Castor Oyl-ish inventor and his harried wife, which are more typical genre entries (Bringing Up Father by way of Rube Goldberg) but have their own energy and verve.
Throughout it all, Segar's art is energetic and expressive, the printed-page equivalent of the black-and-white cartoons of the '20s, and his characters are broad and exciting but always identifiable. Popeye in particular has depths that later stories rarely dealt with: he's a brawling, gambling roughneck of a sailor, but he also has a huge soft spot for children and "brunecks" and a suitably Depression-era easy-come, easy-go attitude towards money. Seger's Thimble Theatre stories are great American originals, and they suffered the fate of every other great American original: to be watered down and redone a thousand times by a thousand hacks in search of a quick buck and a sure thing. But the original endures to be rediscovered, as often as necessary, and that's no small thing.
 After I typed this, I happened to look closely at the spine, where "Volume Two" also appears, in teeny-tiny type near the bottom.
 Its immortal first sentence:
From its inception in the mid-1910s, Elzie Crisler Segar's Thimble Theatre kept in mind that it was a theater indeed; and the outstanding result, and wondrous paradox, of this belief was that even the original cast -- Olive Oyl; her ferrety brother Castor; her staid, forbearing parents Nana Oyl and Cole Oyl; and her fiercely disconsolate suitor Ham Gravy -- occupied the foreground of the strip in physical presences, and, a fortiori, as it continued, and their proper demons entered them, their personalities.
Book-A-Day 2010: The Epic Index