When considering lenght of retirement, Foreman is in an unsurpassed class of his own. When considering accomplishments during the comeback, Ali and others get into the discussion
The question wasn't about impact. It asked "what are the best comebacks after 3-year layoffs?". If you feel nobody but Ali or Foreman had a meaningful or impactful comeback, fine, but you can still discuss whose comebacks were the best after theirs without attaching some deep historical significance to it. For instance, my nominee, Popo Freitas - his comeback in the grand scheme of things doesn't matter. Sure, he upset a ranked unbeaten guy - but Oliveira was ranked at middleweight (a division where I'm pretty sure Popo never had designs on campaigning, and hasn't since) and it proved to be a one-off. Even had the victory earned him a spot in the junior middleweight rankings, I don't think Freitas' plan was to stick around (indeed he seems to have chosen not to, whether it was or wasn't his plan) - just wanted to shut up a brash kid that was mouthing off calling himself the best thing outta Brazil in years, and pound some respect into him. Mission accomplished. On the world scene? Means nothing. But viewed in a vacuum, considering all the factors (the length of his retirement, the big jump in weight class, the fact that Oliveira is a puncher as well as the much larger man, and so much younger) the comeback itself was very impressive.
Frankie Duarte - took off 3 years after extended drug use, came back to win the Stroh's tournament, the NABF title and fight twice for the world title. Not too shabby.
Two-division champion, four belts altogether. Unified at 130lbs. 10 successful WBO junior lightweight defenses. 13-2 (9 KO) in World Title bouts. Victorious over Casamayor, Grigorian, Raheem, and Barrios along with a solid next tier (Jauregui via 90 second blitz, Attah, Kotey, Ramirez, Saucedo, etc). Unbeaten for nine years straight from his debut. Lost only to a younger, much bigger, and nearer prime Chico (then coming off his own W over El Cepillo, and right before his career-defining W over JLC) and unbeaten 23-year-old Baby Bull, in his thirties, in a unification, coming off a year layoff...and both the Diaz and Corrales fights were competitive before Freitas quit. ...and there we have the rub, and the reason some fans dislike Freitas, and the reason you're probably hesitant to say he was anything near great. Yeah, he quit. More egregiously, he proved the first time no fluke by doing it twice. He quit in fights where he wasn't hopelessly behind, making it even worse. I get it. Fans don't like quitters in the ring. Duran, however, said "no mas" and pretty much gets a pass. I'm not suggesting Freitas was anywhere near as great, and he obviously didn't accomplish half of what Duran accomplished, but he did have a lengthy and notable career which shouldn't be defined by the footnotes of making two questionable judgment calls (granted, even the same one twice) at the very end of it. EVEN IF you found the above to be unpersuasive, bear in mind that after the Diaz quit-job, after getting fat and happy in retirement for over five years, he returned - jumping from 135lbs to 154lbs - to pop the cherry of a puncher ranked #13 at middleweight - and did so by going toe-to-toe. Just proving my point that it was as ballsy a comeback as you'll find. If that doesn't exonerate him for his past sins and restore his "warrior" credentials, I don't know what could. Is anyone other than Roberto Duran irredeemable for the same misstep?
Mind you, I never slapped the "All Time Great" label on Freitas... I said he is the greatest Brazilian since Jofre (which is undeniable) and greater than any before or after. He isn't ATG, but is borderline HOF worthy.
Eder Jofre's comeback is so overrated. He had 25 fights but just one was against a top-tier opponent. That, being Jose Legra. Jofre beat Vicente Saldivar who was fat and hadn't fought in over two years. Octavio Gomez wasn't a notable featherweight anymore. He was 1-2 over his last three fights—both losses by knockout, including one to a nobody. And the Jose Jimenez win was two years too late. He was decidedly shot since his loss to the Italian Elio Cotena. Jimenez would also go 3-4-1 immediately following his fight with Jofre. Saldivar's brief comeback to beat the two best featherweights Legra and Johnny Famechon after a two-year retirement is more impressive than Jofre's final 25-fight stint.
Oddly enough, Dempsey qualifies for this discussion… even tho he wore the heavyweight crown the entire time and was performing the most egregious duck act in the history of sport.
I thought of Dempsey, but I don't know if it was one of the "best" comebacks. He went 1-2 in three bouts and won two (maybe three) rounds (of the 27 fought) in those three fights. Then again, he made a lot of money, and those three fights were probably the most high profile of his career.
Foremans comeback ranks over Vitali's comeback. Moorer >> Peters. That WBC belt was trading hands and being fought under vacancy by the worst wastemen the division has seen. George won the HW Championship in one of the best HW ear's of all time.