Answer: Obi-Wan
With Palpatine exposed as Darth Sidious, and Anakin exposed as Darth Vader, Yoda and Obi-Wan set out, individually, to confront and destroy the two Sith Lords. (Obi-Wan and Yoda are the only known survivors of a Sith/Clone attack on the Jedi.) After a gruelling duel, Obi-Wan leaves Vader legless, badly burned, and dying on the lava planet Mustafar. Vader is, of course, saved by Darth Sidious after Obi-Wan has departed.
Interesting note: In this scene Obi-Wan cries, "You were the Chosen One!" This indicates Master Kenobi believed Anakin failed to fulfill his destiny. However, earlier in the movie, Yoda indicates the Prophecy about the Chosen One may have been mistinterpreted. The Prophecy stated that the Chosen One would bring balance to the Force, and destroy the Sith. Many Jedi interpreted bringing balance to the Force, and destroying the Sith to be the same event. However, the Sith had been in hiding for a millenium and were thought extinct before the emergence of Darth Maul in "Episode I". The Force indeed, had been out of balance, as the Jedi had been unchallenged by the Dark Lords Of The Sith for a thousand years.
When Anakin (Darth Vader) helped Darth Sidious destroy the Jedi, and take complete control of the Republic/Empire, the tables were turned. In "Episodes IV-VI" it is suggested that Vader hunted and killed the few remaining Jedi in the years between "Revenge Of The Sith" and "A New Hope". Only two Jedi remained: Obi-Wan and Yoda. There was an actual mathmatical balance: 2 Jedi, and 2 Sith.
In "Return Of The Jedi" Darth Vader returns to the Light Side and kills Darth Sidious, effectively destroying the Sith.
Thus, it is plausible that the prophecy has been fulfilled, as two distinct, separate events, and that Master Yoda was right about the misinterpretation.
CORRECTION NOTE: I have only said this theory is PLAUSIBLE, not cold, hard, Lucas-endorsed fact. Further, I am aware that the novels after "Return Of The Jedi", suggest that other Jedi successfully hid and survived through the original trilogy, and that Emperor Palpatine returns as a Sith Lord in a cloned body, and that Vader had a secret Sith Apprentice who continued the order. However, these happenings are a part of the "Expanded Star Wars Universe", and are not necessarily a part of Lucas's vision. This "extra info" is based solely on the events of the six episodes that make up the two Lucas trilogies. The very name "Return Of The Jedi" suggests there are none after Yoda's death, and that Luke becoming a Jedi at the end of the movie is the return of such. Sorry for such an extensive, pre-emptive note, but I know how picky we geeks can be, and would rather type it once than reply to several correction notices.