Hagler's chin was so good that his head would get pushed before he got rattled, against Hearns, some combinations and hits made it look like they were fighting on a slip and slide.
Keep in mind that Hagler faced guys wearing 8oz gloves while Golovkin faced guys using 10 oz modern gloves.
GGG has probably the best chin I have ever seen. I don't recall him ever being rocked. He ain't being KO'd by any middleweight. Not a chance.
I wouldn't favour anyone to stop GGG at MW, but an RJJ body shot is probably the best chance. Gennady's chin is cast iron and RJJ theoretically had enough speed to land a power shot to Golovkin's body that he didn't see coming...
I think Golovkin is one of those guys that can't be stopped. Beaten..............yeah there's a number. Stopped? Nah.
I seem to recall Derevyanchenko hurting Golovkin to the body in their fight, so if i was going to pick anyone to stop Golovkin it would be someone like McClellan who was a lethal body puncher and a genuine 1 punch KO artist. @Greg Price99 also mentioned RJJ who isn't a bad shout he was also a huge puncher at Middleweight who is noted for good body punches see the Hill fight. Jones also stopped Thomas Tate in just 2 rounds at Middleweight, who went 12 rounds with Julian Jackson and took his best punches. So maybe RJJ could surprise Golovkin with his speed and catch him with a shot he isn't prepared for. I still wouldn't bet on Golovkin being stopped though but the 2 above are good candidates to attempt it.
Against really powerful and dangerous fighters Golovkin turns up his defense and alertness IQ to go along with his great chin. So no, I favor him to hang with any of them. The one fight that alot folks thought might be the time GGG gets stopped was the trilogy fight when GGG went up in weight vs a powerful super middleweight champ at the age of forty years old. Canelo vowed to stop him and retire old GGG. That fight only enhanced GGG'S reputation for having a great chin, as Canelo couldn't hurt him at all.
Which fights exactly did he come into the ring in the 170s? The IBF same day weigh-ins required him to be below 170 and the fights I've seen of him which reported his fight night weight put him usually somewhere around 168, like the tale of the tape at 2:36: This content is protected There are reports of him being 170 bang on for Lemieux and Monroe but these seems to be little evidence for this. Gennadiy stated that he started camps weighing in at 168 or 170 so the idea that he was a big MW is a myth imo.
There is no way he survives Julian Jackson punching with a 8oz glove. Curtis Stevens was a good puncher but no comparison.
RJJ was only stopped at Light Heavyweight not Middleweight or Super Middleweight. And that was at 35 years old after dropping down from Heavyweight against a big punching Southpaw Light Heavyweight who has stopped Cruiserweights & Heavyweights.