Yeah, pretty much what Christopher said - we encounter Early early in the flick (har har...), after he had already become Harry's partner. I do like his character, and he and Harry seem to have mutual respect for each other. Perhaps they made Early a black character to balance out Popwell's role as JJ the pimp, in order to not stereotype them as always being the 'bad guys,' as Dirty Harry was accused of doing.
Could you imagine Popwell being his regular partner? I think his face & looks were too intimidating, and they effectively placed him in roles that took advantage of those looks. He made a great bad guy, although he was enjoyable as a good guy in Sudden Impact.
But staying on subject, it is sad when Early dies, makes you wonder why the writers had him killed him off so sudden. But that just re-emphasizes what has been mentioned before, that the "righteous" vigilantes had no problem murdering their own if it served their interests. Early is my second favorite partner (next to Chico), and unfortunately he is taken out of the picture too soon I feel. Personally, I don't think his & Callahan's relationship is an important part of the story, but like I said, Early is a very likable character who risks his life (and ultimately gives it) in upholding the law.