Master Yoda knew that Darth Vader was once Anakin Skywalker- the boy he sensed too much fear in to train way back in Star Wars: The Phantom Menace. For many years it's been assumed Master Yoda was aware from the day Vader gained his cybernetic enhancements and signature wheeze.
While Darth Vader and Jedi Master Yoda never fought in the official Star Wars canon, an alternate timeline from Dark Horse Comics pitted them together with a rather unexpected ending.
This information comes to light form the comic series Darth Vader: Dark Lord of the Sith by Charles Soule and Giuseppe Camuncoli, in particular issue #7. Palpatine admits to Darth Vader that the Jedi he actually feared most was none other than Jocasta Nu.
Fighting Emperor Palpatine
Though Yoda was able to keep his adversary on his toes, he was unable to end the conflict, and their duel ended with no clear victor.
Yoda held the title of Grand Master of the Jedi Order since the days of the High Republic Era. At some point, Yoda took on a human named Kantam Sy as his Padawan. The two were stationed at the Jedi Temple on the planet Endovar.
Because he was not an active member of the Jedi Order during Order 66, Infil'a escaped execution. Some time later, he faced the Sith Lord Darth Vader wielding a green lightsaber. Infil'a put up a fierce fight against Vader, almost killing him by throwing the Sith Lord off of a cliff.
1/15 Luke Skywalker
Having faced his father once before, Luke was familiar with his tactics and used the force to gain an upper-hand. In Star Wars Canon, only Luke Skywalker can be acknowledged as the one who truly defeated Darth Vader.
Vader held respect for Tarkin which is clearly shown and the only case in which Tarkin outranked Vader would be the case in which Vader was in the Death Star or within Tarkin's Oversector which he likely was as Tarkin was Grand Moff of the Outer Rim Oversector, the largest one.
Over the years, Anakin came to highly respect Yoda, while Yoda gradually outgrew his fear of Anakin and came to have faith in him and correctly came to believe that Anakin was the Chosen One from the Jedi prophecy.
The Skirmish in the Senate was a confrontation that took place in 19 BBY between the Dark Lord of the Sith Darth Sidious and the Jedi Grand Master Yoda. The two veterans of the Force engaged in a ferocious lightsaber duel, with each making liberal use of their powers.
His armor could be hacked and controlled by a device. In a turn of events, Darth Vader's right limb holding his dangerous scarlet lightsaber was moving of its own accord toward his neck. This was a dangerous weakness indeed.
The ever stronger fear
In the Phantom Menace, Master Yoda senses much fear in Anakin, however, this fear is not the understandable anxiety - Anakin is afraid to lose his mother, Shmi, whom he was forced to leave behind in slavery.
Had Yoda and Darth Vader fought each other both at full power, the fight arguably would have landed in Yoda's favor. Both are proficient with a lightsaber and with the Force, but Yoda might just be a little bit better.
Darth Sidious
In the end, Vader managed to fulfill the prophecy tied to him. As for Darth Sidious, he's by far the most dangerous enemy Vader has had. Becoming emperor of the galaxy and crushing most of the Jedi was proof enough.
Did Darth Vader ever lost a fight? Darth Vader is one of the greatest villains of all time. But even he gets beaten sometimes. CBR lists all of the folks who managed this improbable feat!
Obi-Wan Could've Beaten Vader in Star Wars: A New Hope - If He Wanted To. While Obi-Wan Kenobi was frail by the time of Star Wars: A New Hope, he was still stronger with the Force than Vader.
Admiral Ozzel : [appearing onscreen with Captain Piett] Lord Vader, the fleet has moved out of lightspeed and we're preparing to... Darth Vader : You have failed me for the last time, Admiral! Captain Piett?
Darth Vader defeats Darth Maul. The two Sith Lords engaged in a lightsaber duel, going through the volcano and onto a bridge situated over a river of lava, which collapsed, though they both survived and continued their battle.
The Force: As the Chosen One, Vader was immensely powerful and had an amazingly strong connection to the Force, stronger than any Force-user ever in existence. He also possessed the potential to according to Obi-Wan Kenboi become the most powerful light and dark side Force-Sensitive being in the history of the galaxy.
Notable Victories: - Shot and apparently killed you to fuel his ketamine addiction.
The second time Yoda mentions his long life is in Return of the Jedi, when he tells Luke, “When you reach 900 years old, you will not look as good as you will.” If we take Yoda at his word, that means the Jedi Master died at the ripe old age of 900.
Mission to Mathas. Padawan Windu was trained in the ways of the Force by Jedi Master Cyslin Myr.