Jerry Whitworth wrote:Before Crisis, there were a number of characters that were almost identical on Earth-1 and Earth-2. Hawkman, although looking the same, had wildly different origins (one was a re-incarnated Egyptian royal, the other an intergalactic spaceman). After Crisis, in perhaps an unpopular move, it was decided the Hawkman that would remain is the Golden Age one. However, people wanted the Silver Age one, so Hawkworld was done. Only, Hawkworld was pretty dark for the supposedly kiddy DC and also people preferred the original space Hawkman. Now, the vast majority of confusion over the Hawkman character came when he appeared in the Justice League. You see, the original was retired, like the rest of the JSA in the wake of the HUAC hearings. The other one was embroiled on Thanagar. So, who was the guy on Earth? With the Invasion! event, it was decided the Hawkman on Earth was in fact an agent for the advancing Thanagarian forces. However, for some reason or another, he pretended to be Katar Hol, even though AFAIK Katar had never been to Earth at this point. Katar would later come to Earth and end up joining the Justice League. But, then people started writing stories about the old League where Ollie and Hawkman fought. Only, it didn't add up because Fel Andar wasn't around at that point and even if he was, that meant all those memories were now clouded by the fact he wasn't Katar. So, needless to say, it was a massive cluster ****. Writers later tried saying it was in fact the Golden Age Hawkman, but by then people were sick of the headache of Hawkman's origins. In fact, rumor has it DC unofficially put a label on Hawkman as "do not touch."
Now, another character who got royally messed with because of Crisis was Dr. Fate, whom IIRC went through five possessors in less than 20 years. But, then in walked David Goyer and James Robinson. They did something rather unique: they actually used DC continuity as a story-driven force instead of acting like it was a leash. Their initial JSA run returned Dr. Fate to prominence and explained the reasoning behind the character changes over the years. Robinson bowed out of JSA and gave his spot to Geoff Johns, whom many saw as a similar writer who liked continuity and put a new spin on things. It was under Johns and Goyer on JSA that the problem of Hawkman was tackled, and after cleaning up Fate, people were really behind the idea. So, he went about tackling the problems and almost making a guide cleaning up Hawkman.
One of fans major Hawkman complaints is the randomness of having a Egyptian Hawkman and a space Hawkman. JSA explained this is because a Thanagarian craft crash landed on Earth in ancient Egypt and not only inspired Khufu (Hawkman's initial incarnation) but also provided his Nth metal.
The next major complaint came from something Zero Hour did. You see, Hawkman and his love and bitter enemy all died in a magic ritual that forces the three to keep re-incarnating and repeating history. But, Zero Hour said that Hawkman was actually a hawk avatar and Vandal Savage's nemesis across time. Johns initially started to clean this up by saying Nth metal actually manipulates the four Fundamental Forces (gravity, strong force, weak force, and electromagnetism). By this, he explained it is the magic ritual and the Nth metal that was used to slay the three that binds them across time due to the effect of the weak force (which is kind of described as decay or breaking down of energy; the Nth metal re-inforces the trio's spirits, which is essentially energy, thus, with the help of the ritual, is what keeps looping them back to life). Johns also did away with the complicated hawk avatar idea in his Hawkman solo series, putting it all on the Egyptian ritual. This explains why so many incarnations of Hawkmen gravitated to Nth metal on Earth, because they were in fact drawn to it.
As for years later, he said it was in fact the Golden Age Hawkman who joined the League and it was partially due to the Nth metal that he was so young in body while there because of the Nth metal lessening the effects of age. Fel Andar was only in the League for a brief time before being outed, this time immitating Carter.
His final step was by combining the two separate Hawkmen. Simply put, we learn that both Hawkmen were destined to be the saviours of Thanagar. Through a ritual on the planet, the then dead Hawkmen were forged together to form one soul, thus giving birth to the new and current Hawkmen who remembers all their past lives. Because of this, we have one Hawkman that essentially fits the bill for all the Hawkmen. This is one of the reasons Johns is so well-received, he takes a problem and fixes it. He's the carpenter of the DCU.
Hope this helps!