We have a moderator in our community, and he is a great strength to us. He's smart, knows what he is talking about, and is very knowledgeable in our field.
But he is very forceful when he knows that he is correct; and will delete other people's posts if they are wrong or contradict him. This is making a small part of the community angry.
How do I as an admin fix this issue without provoking him? He is rather prone to anger and I would like to keep him on the moderator team.
Don't worry about making him angry. If he can't deal with getting on board with helping the community and allowing competing views without getting angry and quitting, then he is not a good moderator, no matter how much of a resource he may be.
Being a good resource and being a good moderator are NOT the same thing. A moderator needs to be able to deal with conflicting views (yes, and even incorrect ones) and exercise good judgement and be able to dispassionately remove themselves from the situation. If a user has an ego, doesn't deal well with dissenting opinions and gets angry easily, then they really are not a good moderator. They may feel like a good resource for the community, but they will eventually do more damage than help. (Such as by driving off other skilled users who don't want to deal with them.)
That said, you don't need to be overly aggressive with him either. Make a strong, logical argument as to why it is a problem (pointing out how it impacts other users and the community) and why it needs to stop. If he argues and you are in a position to do so, simply let him know that he is alienating users and it is a problem that needs to stop. If he understands and changes behavior, great, you misread him and things can continue on. If he gets upset and quits, oh well, it was probably inevitable anyway and the community can get back to a healthy point.
To expand a bit on AJ's answer, moderating a community and judging the technical accuracy of user-submitted content are distinct roles. Your question is an excellent example of the dangers of treating them as one role.
Under no circumstances should a user who is "prone to anger" be given the responsibility to moderate a community. No matter who they are, no matter how much you like them, and no matter how involved they are in the community. Moderation requires impartiality, patience, the ability to keep a cool head. There are many equally important roles that do not.
The problem may not have been apparent when the user first took on the role. As an administrator, you have the unenviable responsibility of correcting their behavior, even if that means removing them from the role. That's the nature of administration; you implement and manage the other roles in the community.
It sounds like you need to implement another role for technical experts in your community. This role should have as little overlap with the moderator role as is practical given the nature of your platform. Technical experts absolutely should not have any exceptional power to delete or alter user-submitted content. If users in your community have the ability to vote on content, you might consider giving your technical experts more heavily weighted votes. If users have the ability to flag content, such as spam or hate speech, you might consider giving your technical experts more heavily weighted flags. You could then pass the responsibility of acting on those votes or flags to your moderator team.
Some platforms deal with "wildly incorrect" and/or "wildly unpopular" content by hiding or de-emphasizing content that exceeds some threshold of negative votes or flags. Here on Stack Exchange, for example, answers that receive very negative net scores are sorted to the bottom and additionally grayed-out to emphasize their status as wildly incorrect and/or unpopular. There is often no great way to distinguish incorrect from unpopular, when everyone in the community can contribute toward this status. This is where technical experts, selected for their ability to judge factual correctness, could play a useful role.
One approach is to simply give this role visibility so that when a technical expert says, "You're wrong," they have some extra credibility. Another approach would be to implement some sort of special content score that can be influenced only by technical experts. Yet another might be to allow your technical experts to put a "black mark" on content that they judge to be inaccurate; by consensus, by separate action, or however you decide works best for your community.
However you go about it, I agree with AJ that this user is not being a good moderator. Your first step should be to communicate with them and try to convince them to change their behavior. Sometimes this will solve the problem on its own. In other cases it won't, but you owe them that courtesy before booting them from the team. Acknowledging their contribution by giving them another role and responsibility that aligns better with their particular skillset might soften the blow a bit.
If you're the administrator or owner of the forum then he should be worried about angering you. If his ego is so inflated that he feels the group can't live without him then test it yourself and you'll see that it can.
I'm a moderator of a few groups and right or wrong I leave the messages up. If the messages violates the rules stated by the group administrator or owner then we lock the thread and the last message up states why and any replies go to a moderated hold and just sit there but the moderators will still see the replies to hear anyone out.
He's not the group owner or administrator and he needs to know that. You can politely let him know and if he has anger management issues then it might be best to severe the ties regardless of how helpful and knowledgeable he's been in the past. He's not the final authority of knowledge otherwise he'd be the administrator or owner of his own group setting down the laws of his land...
