My best guess is that as an author, he is thanking his agent - the person who is responsible for finding a publisher to publish the author's work, and negotiating the payment they receive (at least, I assume that is what agents do). So I guess that John Smith is the author's agent, and the use of 'summa cum laude' is a way of saying the agent is superior to all others. I also suspect the author is American, as I believe this title is used in American universities. Someone else might have expressed the same sentiment by saying '..John Smith, agent extraordinaire'.

I have no idea. Gary is right that Summa cum laude is the highest honor university students can be given, and it is derived from Latin, but 'agent' is very strange and I've never heard it before.

Thank you so much, Gary

It was mentioned in a fantasy book acknowledgment. Through out the acknowledgment the author was thanking a lot of people for helping him avoid being slain by monsters and was likening some of them to Greek gods and goddesses.

It sounds to me like a pseudo-honorific.