We don’t know. According to The Walking Dead Wiki, ‘Nothing is known about Negan’s life before or as the outbreak began, except that he enjoyed billiards and ping-pong and used to be a used car salesman.’
So aside for once having a job as a used-car salesman, what do you think he did for a living? The first thing out of Mrs. L.A.'s mouth when I asked her was ‘He was a cop.’ She then said she didn’t really think so, but I don’t think it’s beyond the realm of possibilities. And as Mrs. L.A. said, they do like to draw parallels on the show.
See, I disagree with the comparison to The Governor. Negan is very disciplined and has a system he has created that is consistent. He isn’t erratic or mentally unstable like The Governor, acting impulsively and/or risking and losing everything out of vengeance or ego. He has created an ordered society with rules, yes he enforces those rules ruthlessly, but there are rules and known outcomes. He has a strategy for how to deal with new survivors or groups and it is fairly pragmatic from The Saviors perspective. You will submit and work for Negan, providing him half of your shit which (I assume) is used to then feed and equip The Saviors who are loyal to him. To demonstrate in advance the consequences of not submitting, a member of the new group is brutally killed as an object lesson. However from that point, there is no animosity or further violence unless you refuse to submit and live according to his New World Order. From a certain point of view coughBenKenobicough it is perfectly logical and ordered.
I’m not saying I’d like to live under that New World Order tho’.
