What is the point of this character? For what purpose does it exist?
I think, story-wise, you're very much intended to be a blank slate. You were abducted by mind flayers and implanted with a parasite. *This* is what makes you special. I mean, think about it: one of the first encounters that you can have is with a group of fishermen that have been mind-controlled. If you try this encounter without companions you'll *probably* get your ass handed to you. You're basically a barely-competent adventurer. For that matter: the opening cinematic features the mind flayer ship just snagging every Tom, Dick, and Harry it can off of the street of Baldur's Gate. As far as we know thus far: there's *nothing* special about you, you were just thrust into this situation and have to make the best of it.
That being said: your character doesn't lack distinguishing features and they're not completely "blank." What I've noticed in my multiple playthroughs is that the selections you make at the start of the game are actually fairly impactful RP-wise, much more than I expected them to be. If you're playing as a Githyanki you'll find several skill checks that you simply bypass because your whole species has dedicated themselves to hunting mind flayers, so naturally you know quite a bit about them. If you're a rogue you'll immediately comprehend what's happening when you encounter someone trying to swindle you and be able to call them out on it. Your background, class, and selected skills *do* have an impact to an extent that I certainly didn't anticipate coming into the game.