Yes, the movie was great I saw it too. Phil Gordon, in his book "Poker the real deal", talks about "the kid" in the 1st chapter of this book, describing him as having a "photographic memory" and a "genius IQ".
The most interesting part is this one: "He dropped out of school at 15 to become a professional gin rummy player...destroying himself in the process with heavy drug use and heavier sports betting. By the time he got to Las Vegas in 1976, the 23 year old was dead broke. Ungar somehow scraped together the buy-in for a $50.000 gin tournament. He won, of course, but couldn't resist forecasting each of his opponent's cards on the final 2 hands in front of a crowd of gaping onlookers. A scary feat, enough to frighten anyone from playing gin rummy with the kid, or at least for any serious money. It would end his gin rummy career."
He then describes the wins at the WSOP and also his success in NLHE.
Overall he must have been some character besides being incredibly skilled, unfortunately his addictions ended up getting the better of him.
I'll definitely check out the book.
I want to conclude with a quote from Chip Reese, also found on Gordon's book: "If you think about what money can do for you, you're gone. That's what made Stuey Ungar such a great no-limit player: He never, ever, ever cared."