I've seen a lot of queries where the writer starts off with the main character's full name. "Dr. Felixandro Buttonweezer III was just your average shark researcher until..." Then they're called by nickname for the rest of the query. "Felix must battle through Character Soup and Plot Salad before he's free." I can understand people doing this if the character's title or family name is important, but I see it all the time. Is there some grand unwritten rule about this? Should we just start off with Felix if we're going to call him that anyway? Or is it one of those "whatever works for the rhythm and tone" problems?
I've seen this a lot too, and it doesn't stand out as something I'd suggest be changed. Thus it's one of those "whatever works for the rhythm and tone" items.
However, there are a couple things writers do when introducing characters that do drive me batshark crazy:
(1) Dr. Felixandro "Felix" Buttonweezer III
If you're going to call him Felix, do it. If you're going to use his full name, do that. But do NOT combine them. That's newspaper style writing, and you're not writing an article for the SharkVille Times. You're writing a letter.
(2) Dr. Felixandro Buttonweezer III, 34, was just your average shark researcher
Again, adding Felix's age after his name is like newspaper writing. If his age is important, tell us when it's important. Dr. Felix Buttonweezer was only 34 when Mrs. Buttonweezer started planning for his retirement.
In one place it's part of the story, in another it's just an isolated fact with no context. You do NOT want isolated facts with no context in a query. Every piece of information should be part of the narrative. It should be there for a reason.
(3) Felix and Felicia were twins. The Buttonweezer clan thought twins were bad luck.
In a query, which is very short form, and often skimmed, you want to make rock solid certain that your reader isn't confused. Here, there is confusion because we don't know if Felix and Felicia are part of the Buttonweezer clan.
This is how you fix that: Felix and Felicia Buttonweezer were twins, something the Buttonweezer clan thought was bad luck. Even though you use the Buttonweezer name twice in a sentence, it's CLEAR. Clarity is the goal.