Star Wars canon points to Anakin Skywalker being the one who brings balance to the Force. Please follow this link here to see expanded discussion on what the prophecy actually means regarding balance to the Force, and whether or not it was even fulfilled.
George Lucas, in the commentary of A New Hope stated:
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...
This proves that "balance" does not necessarily mean equal number on both sides. The answer in the link also states:
...the prophecy probably means that Anakin would bring harmony between the two sides of the Force, which requires the destruction of the Sith whose aim was to destroy the Light side.
The user admits during his conclusion that there isn't even total agreement on whether the prophecy was actually fulfilled. The answer to this question gives great insight and evidence as to how the Sith unbalanced the Force in the first place, creating the need for it to be balanced.