[lutusp]

> Unban him from the forum. Then he'll (maybe) stop.

This is a very, very bad idea -- it's on a par with negotiating with terrorists.

> Maintaining control over your life and online reputation is more important than keeping him banned.

You seem not to realize that, by giving in to blackmail, one surrenders control of one's life to the next person who wants to engage in harassment. Also, what's to stop the original perpetrator from gloating about his victory over you and resuming or escalating his unacceptable behavior?

No, this is not an option.