As someone who is often perceived to be too negative or worse (although I've improved a lot over the years), I can tell you that in terms of the options you're

As someone who is often perceived to be too negative or worse (although I've improved a lot over the years), I can tell you that in terms of the options you're considering, the best solution is different, but does involve #1. First, recognize that not everyone thinks the same, or has the same style. Consider that just like his attitude upsets you, your (or your coworkers) attitudes may be upsetting him. This is key to coming up with a solution that works for everyone. Second, understand that this is probably more venting than anything. The guy is getting frustrated and knows he can't (and shouldn't) take it out on people he sees as having messed up. This doesn't make it right, but consider that the guy is trying not to be toxic. Third, the guy needs regular feedback about this. --You mention that when your manager talks to him, things improve for a time. This ties into my second point, that the guy is actually trying. You may or may not be in a position where he'll listen to you. I'd recommend trying to talk to him about this directly. When you do this, don't beat around the bush. --Tell him that you know he's good at what he does, but that the constant complaining about coworkers makes it hard for you and others to work with him. I really recommend that you do this. Or if not you, the coworker who he seems to have the most respect for - it'll often mean more coming from a coworker than a manager. Fourth, ask your manager to follow up regularly. --He needs to help keep reinforcing the attitude change so that the guy doesn't fall back into old habits. Finally, consider offering the guy a chance to vent over lunch once a week or so away from the office. --This helps give him a chance to get things off his chest, but to do it somewhere that it doesn't hurt others. And it might give you a chance to give him some insights of your own about the people he complains about. This guy may never be your ideal coworker, but you can probably help find the middle ground that makes things better for everyone.