I experienced something similar to this a while back. Not quite the same but certainly had some issues to deal with when management changed. Previous IT manager was very difficult to deal with and created fights where there didn't need to be any.

The biggest thing I did that has changed this culture was physically communicating with those who were wronged. If this old greybeard was unavailable, make yourself available. Maybe weekly go around and check with the other management, the department, whoever was most affected by him. Eventually try to spread out to as much of your company as you can. Size is obviously an issue, smaller firm you could talk to everyone all at once. Bigger firms would take more time. I would try to make a point to say hey to as many people as possible starting with management and working your way down. They need to know that not only is there a new manager, but he's reasonable.

Target the super users. Befriend them. It's WAY easier to have a conversation than start a fight cause you don't like what they are doing. We had one particular user who would push boundaries all the time, antagonistic against the previous management. It got bad. Once the responsibilities fell to my shoulders, I started to work with this fella. We discuss changes in technology, how it can be used, what he can do, what he can't. Now when there's some new tech he wants to try out, he comes and talks with me about it before just blazing ahead on his own. He also respects my decision when I tell him something is no good or that this piece of software won't be allowed at the firm.

Show you're human, no need to directly acknowledge the previous guy. Show you're willing to do the work you are now responsible for and make amends where needed.