The only child of a wealthy merchant family with delusions of nobility, Riddle spent most of his early years being bullied around by sons of Proper Nobles. In his efforts to avoid this, he developed some basic skills of stealth and, well, Breaking & Exiting. His parents made sure he got tutored in the use of a rapier ("it's a gentleman's weapon"), but he would still rather avoid confrontation than go around slapping people with gloves.
That said, he's always taken insane risks to "borrow" any books he could get his hands on. He'd break into the old clock tower, and sit there reading of a world where the most exciting thing was *not* a dinner invitation to the LeQuille's. Where there was surprise, danger... and magic.
More than anything, Riddle wants to be a wizard. It's the one thing he might truly go to extremes to achieve.
He dislikes anything that smacks of pretense - chivalry, etiquette, religion - but is generally rather timid, polite and easy-going. Unless you get him started on the topics of the Rights of the Gentry, Divine Magic, or the properties of quicksilver at extreme temperatures. (Yes, he is blissfully unaware that his own animated rants could be viewed as pretentious - Riddle may be smarter than your average Illithid, but he's also about as perceptive as a troll. And only a bit more of a people person - he's never been the life of the party. He's the guy in the kitchen coddling the double shot of Dwarf Whiskey, who *wishes* he was That Bloody Foppish Bard covered in ladies. Except noblewomen bore the nine hells out of him.)
Like many who grew up with wealth but shunned it, he idealizes the honest, hard-working, salt-of-the-earth types. Wants to be one of the "real" people, but is painfully aware that his upbringing leaves him with a foot in each world, never truly at home in either.
So he tries to make his home on the road. Earns his living by selling alchemical concotions. (A skill he picked up from his uncle, who also gave him the nickname - because of his fondness for puzzle-solving and the like.) He's tried to get mercenary jobs, but so far - being quite plain-looking and not too gifted in the brawn department - it's been hard. The goal is to amass enough money to get into a wizard school. Or, even better, find someone willing to tutor him.
It's not that Riddle wants the power; he loves magic for its own sake. At least, that is what he tells himself. But many things can happen along the way.