Correct guesses for me:
Mario Lemieux
The Kool Aid man
The Queen of England
Bender (from Futurama)
Akinator (only 8 guesses for that one 
JRagon, it does actually expect “don’t know” or “probably” answers for some people. At the end of the game, if he guesses right, you can click on “game report” to see what answer he expected for each question, and there are often a few of those in there. For example, he gets Vaarsuvius pretty quickly, because gender is usually one of the first questions and “don’t know” is a rare answer for that one, and once when I tried Nobby Nobs, the last question before the guess was “Is your character human”, for which it expected “probably”.
Didn’t get Judith Durham (guesses were ONJ, Chrissy Amphlett, Lisa Gerrard and Suzi Quatro).
Didn’t get Rupert of the Rhine (guesses were Wellington, Cardigan, Marlborough and William of Orange).
Didn’t get Logan Sackett (guesses were Finnick Odair, Pecos Bill and LaBoeuf), though three other Sacketts were in its list.
Then it might be a tree with a branch for each answer. Either way, I’m sticking with the notion that it’s either a simple tree, or at best a tree with a non-deterministic path (i.e. it picks 2 or 3 branches to follow and slowly discards them).
Didn’t get Tor Johnson (actor in Plan 9 From Outer Space and other Ed Wood movies)
It took one wrong guess, but it got Whacky waving inflatable arm flailing tube man from Family Guy.
It seems to be cheating a bit though, it keeps asking if my character is swedish, I’m guessing it gets that I’m in sweden from my IP…
Just stumped Akinator, who incorrectly guessed the Where’s Waldo guy; “Mr. Monopoly”, whose name is “officially” Rich Uncle Pennybags; and the Joker from a deck of cards. I was thinking of Sylvester P. Smythe, who was in the database and correctly identified as “Cracked janitor mascot”.
Earlier, Akinator correctly guessed Barbara Cooper of “One Day at a Time” after 18 questions.
Stumped it with Polyhymnia O’Keefe, then stumped it again with Polyhymnia herself. Oddly enough the only list choice was the one I’d just submitted - he had already guessed Athene, Demeter, and Persephone.
He got Chen Stormstout from WoW in only a few guesses.
Took him 3 tries to get Dr. Kelly Brackett from Emergency!
I stumped him on Captain Lee Crane from Voyage to the Bottom of the Sea.
It got my namesake in 23 questions. Well, it came up with Dr. Mrs. The Monarch, close enough.
I stumped it with Reubens Barrichello (F1 and Indycar driver) and Bob Chase (Fort Wayne Komets broadcaster for 60+years).
I managed to stump it (on its first guess) today with both Roy Hobbs (from The Natural) and Oddjob (from Goldfinger), but it got both in another 5 or 6 questions.
But somehow it got Jimmer Fredette of the Sacramento Kings. I was impressed.
It got Jonah for me in 20 questions. I did pick him as “real” instead of fictional, so perhaps that throws it?
It got him in 26 questions for me.
I beat it on Bob Elliott (of Bob and Ray, father of Chris Elliott). It wasn’t even close with most questions, and kept repeating certain questions or asking questions that would contradict earlier ones (gender, age questions in particular).
I stumped it on Maurice Pogue, lead character from the largely forgotten Dana Carvey movie, Clean Slate.
It had to ask extra questions to get to Diana Barry from Anne of Green Gables (its first guess was Anne Shirley).
It also missed Iggle Piggle from In The Night Garden though it guessed Makka Pakka (even though I told it my character was blue).
It picked Katherine Howard (wife of King Henry VIII) without hesitation.
It got Oliver Hazard Perry on five questions. I about dropped my iPad.
Stumped Akinator with the Snuggle bear, who was in the database. Incorrect guesses were Elmo, “your teddy bear”, Furby, and Bearemy of Build-A-Bear Workshop.
Got Bob Sacamano (unseen friend of Kramer on Seinfeld) after 25 questions, with no incorrect guesses.
I’m still playing with this…
It got Harry Caray in about 50 questions after first guessing Perry Como.
Looking at the log is illuminating-I tried Herbie the Love Bug, and, while he got it 25 guesses, the log revealed that Akinator thought that “Was your character in a TV series” was a “no”, while in fact there was a (short-lived) Herbie TV series. If the database is faulty and you correctly answer the opposite of what is asked, then he might not ever get back on track to guess your choice.