Pretty well any attribute or intangible you can think of in boxing he did good. He was always consistent in his fights bringing a solid attack in every round. He could fight on the inside or outside and could change up his approach throughout the fight even throughout single rounds he'd change his attack back and forth as well as anyone. His skills were top notch but what truly separated him from the rest was what was inside Hagler had a drive like no one else and wouldn't accept losing he'd rather die. This mentality complemented by his skills, ring smart and dedication made him an ATG.....
If you watch Hagler fight over his career and don't know what made him a top fighter, you don't know enough about boxing.
I don't see why people look at Hagler not moving up in weight as something that takes away from his legacy. I think it's more impressive that he stayed in one class and ruled rather than jump from one to the next. Two modern day examples are Mayweather and Pacquiao, I have nothing respect for both of them, but they have both stopped at one weight class for a fight or two, one a belt and jumped to the next. Hagler stayed in one and dominate it though. Plus there was no super middleweight so Hagler would have had to jump straight to light heavy. He also could have started at junior middle, but he just fought at middleweight and made a spectacular career of it. What makes him great? 12 title defense 11 by knockout all against legitimate opponents, one of the best chins ever, very smart, good speed, good puncher, great punch accuracy, and had all the intangibles, he really was marvelous.
His consistency, drive and all around ability. Very much like Hopkins in that regard. No real weaknesses and very few if any sub-par performances. Not as naturally talented like for example Toney or perhaps even Nunn, but their discipline and consistency more than made up for it.
Because this guy is clearly a younger fan, for whom the idea of a "world title" is meaningless. There's no cache' in them anymore because of how many there are, so the only thing that holds any weight with young fans now is whether or not one moves up and wins titles in multiple weight classes. You just get blank stares from them when you say someone was a titlist at any one weight for more than a year. Don't fault him for this transgression; it's all they have now.
Just to echo comments already made, I always thought it was a plus that Hagler stayed at one weight for his career. How many guys move up because they don't want to make weight. That discipline was one of Hagler's strongest traits. Absolute warrior who brought it every fight. Could box, could brawl, & had the skills & chin to do both successfully.
What made Jordan so great? He only played two sports and excelled in just one. Now, the incomparable Bo Jackson - he was better than mediocre at several. :deal GOAT athlete right there.
His most famous fights were all against smaller guys, dominated an average division, never moved up to take a fight against Spinks, struggled with Vito Antoufermo and lost to a semi-retired Ray Leonard. Hagler was a very good fighter, but he's the most over-praised fighter on these forums. Even suggesting that any other 160 pounder in history could have been competitive with him is considered blasphemous by some here.
I feel that Hagler should actually be 63-3-1. He beat Antuofermo in their 1st fight but was shafted with a draw. But anyway there's no denying the fact that Hagler is an ATG. He could box or slug, was always in great shape, had a concrete chin and an incredible will to win. he was champion when there was only 1 middleweight title, not 2 or 3 like we have today which is laughable and he dominated for a considerable length of time. Plus he was a proven 15 rd fighter at at time when 12 rounds is what an up and coming fighter would fight before going for the title. He fought tough competition while making a name for himself and didn't get a shot after only 15 or 20 fights. A true throwback to the greats of yesteryear.
See, most historians I know consider it a boon rather than a detriment to Hagler's legacy that he fought the other three of the 4 Kings. To each their own, I guess. They were his most famous opponents, yes, but how is the relative lack of fame of his many full-fledged middleweight opponents (many of them quite good, even if not household names like Duran, Leonard or Hearns) the fault of Hagler? You are half right there. Best MW era of all time? No. Average, though? No. You realize by today's standards that is a two weight division jump? That's like criticizing, say, Golovkin, not for refusing to move up for Ward or Froch, but for refusing to up for Kovalev. :-( So what? Antuofermo is a WBHOF inductee, was the champ when they first met, and was a rugged pain in the ass to fight, and Hagler arguably beat him at his own game in their draw: brawling. Not to mention tearing his face half off and stopping him in the rematch. "Lost", controversially, semi-retired himself and with the deck absolutely stacked against him in every conceivable way. Hardly. There are literally dozens of guys whose actual h2h ability doesn't live up to how much they've been enshrouded in mythic adulation. Jack Johnson plowing through modern heavyweights ring a bell? Hagler is legitimately up with the very best middleweights of all time h2h, whether you put him at #1 or not. No serious boxing historian thinks otherwise. No, suggesting that any but the very best would beat him is what's considered blasphemous...and people have on these forums just that, picking the likes of Kelly Pavlik over him. Yet Hagler is overrated? :blood