Anakin was the chosen one. Yoda said "A prophecy that misread could have been" when they were talking about the prophesied one who would bring balance to the Force. When Anakin fell to the Dark Side and became Vader, the Sith was comprised of only two, but the Jedi were many. Vader destroyed the Jedi order which left only two Jedi - Yoda and Obi Wan. He brought balance to the force, but the Jedi were so self involved they didn't realize that they were the dominant power in the Force.
Again. Incorrect. It had nothing to do with balancing the numbers. The Sith were the ones imbalanced. From George Lucas..
"The first film starts with the last age of the Republic, which is it's getting tired, it's old, it's getting corrupt.
There's the rise of the Sith, who are becoming a force, and in the backdrop of this we have Anakin Skywalker, a young boy who is destined to be a significant player in bringing balance back to the Force and to the Republic...
Then in the second film we get into more of that turmoil. It's the beginning of the Clone Wars, it's the beginning of the end of democracy in the Republic, sort of the beginning of the end of the Republic. And it's Anakin Skywalker beginning to deal with some of his more intense emotions of anger, hatred, sense of loss, possessiveness, jealousy, and the other things he has to cope with.
And then we will get to the 3rd film where he is seduced to the dark side..
Which brings us up to the films 4, 5, and 6, in which Anakin's offspring redeem him and allow him to fulfill the prophecy where he brings balance to the Force by doing away with the Sith and getting rid of evil in the universe..."