I work in a niche field, which is normally full of people who mostly collaborate, rather than compete with each other. Lots of small organizations, government entities, and individual freelancers involved. In general I would say this is a nice industry with a lot of well-meaning people.
Unfortunately, there is one toxic individual who combines charisma, defamation, and manipulation very well. I have witnessed him praising people when in their vicinity, and tearing them down when not around. I've seen him take credit of other people's work. He cozies up to people of authority and then runs interference with projects and people he doesn't like through these relationships.
There are two ways in which this affects me. Firstly, ever since I called him out on something, me and my own small organization are now on his blacklist, and I know he's been spreading misinformation to discredit us and our work. This seriously affects our reputation and has the potential to cause severe damage. Secondly, he is really destroying the spirit of collaboration and volunteerism that exists in our community. He pits people against each other, and it is really sad to see how this affects the overall community.
How to best deal with this? He is a freelancer and I have my own organization, and we have no formal authority governing us both in a professional context (other than local government that we both work with as external partners). The main problem I see is his charisma and cunning manipulation skills. A lot of the things he does are under the radar, and carry the risk of "he says she says" dirt throwing. He has already burned himself with a number of people in the field, and there are others who have seen his tricks. However, there are also key people that he is very friendly with who easily take his side. Furthermore, he interacts with a broader public and (at times through lies and misappropriation of work) he carries some traction and is seen as someone "in the know". So again this makes it difficult to start some sort of a campaign to bring out what he has been doing.
What would be a good approach?