Friends and Allies
Yoda trained Mace and he has always held him in high esteem. Mace also deeply respected Yoda and always obeyed him, though he did occasionally disagree with him.
Yoda held Obi-Wan in high esteem and trained him when he was a young boy, prior to Obi-Wan becoming Qui-Gon Jinn's apprentice. Obi-Wan deeply respected Yoda and obeyed him usually without question.
After Obi-Wan died, he entrusted Luke's training to a reluctant Yoda.
Though Yoda and Qui-Gon respected each other, they often disagreed with their respective beliefs; Yoda focused mainly on the future while Qui-Gon lived in the moment. After Qui-Gon was killed by Darth Maul, Yoda was saddened, but continued to disapprove of Qui-Gon's beliefs, regarding them as "defiant".
After he failed to defeat the Emperor, Qui-Gon's spirit taught Yoda the Shaman of the Willis. It was only then that Yoda finally and truly acknowledged the fact that Qui-Gon had been a great Jedi and apologized for not recognizing it.
Like all Jedi, Ahsoka deeply respected Yoda and would usually go to him for guidance when Anakin or Obi-Wan weren't around. Yoda seemed to have a mild fondness for Ahsoka and assigned her to be Anakin's apprentice.
However, when Ahsoka was accused of treason, Yoda, like most of the Jedi, believed she was guilty and sent Anakin and Plo Koon to capture her. When Tarkin demanded Ahsoka to be expelled from the Jedi Order and turned over to the Republic military for her so-called treason, Yoda seemed unsure about doing so, mainly because it was against Jedi tradition to expel one of their own without a fair trial, but ultimately agreed and had the young Togruta stripped of her status as a Jedi.
Like many of the Jedi, Yoda was present during Ahsoka's trial as presided over by Chancellor Palpatine and during Barriss Offee's confession, proving Ahsoka to be innocent. He was surprised that Ahsoka had been innocent the entire time.
Along with the rest of the Jedi High Council, Yoda personally pardoned Ahsoka and invited her to rejoin the Jedi Order, even offering to promote her to the rank of Jedi Knight. However, feeling betrayed because the Council never believed in her and believing she could not trust them any-more, Ahsoka refused reinstatement and walked away from the Jedi Order, a decision that surprised all members of the Order, including Yoda.
Ahsoka's departure haunted Yoda for sometime afterwards; he felt extremely guilty and remorseful, partly for refusing to stand by her and partly for placing her on the path that led to her departure from the Jedi Order. In fact, his guilt was so great that the Dark side tried to use it against him, but failed.
Yoda first met Luke on Dagobah (as Luke was instructed to go there by the spirit of Obi-Wan Kenobi). Luke's first impression of Yoda was that of a strange, yet harmless hermit, however, after spending many hours on Dagobah, he realizes that the green alien was, in fact, a Force-user like himself and the last surviving Jedi Master in the galaxy; he discovers this when Yoda begins to talk to Obi-Wan through the Force. At first, Luke wonders who he is talking to, until he hears Obi-Wan's voice. Yoda initially refuses to train Luke as a Jedi (despite the fact that there were very few Jedi left in the galaxy), partly due to his age and mainly because the be believed Luke to be too much like his father, Anakin Skywalker, in personality (reckless, impulsive, short-tempered and hot-headed).
Yoda was eventually persuaded, albeit reluctantly, by Obi-Wan to accept Luke as a trainee. Yoda then begins to train Luke in the ways of the Light side of the Force and lightsaber combat, but also warns him about the dangers and lure of the Dark side of the Force. Luke had been on Dagobah for at least a year and came to greatly respect the elderly Jedi Master - having the same level of respect for Yoda that his father once had.
Luke has a vision of his friends in pain and leaves to rescue them, abandoning his training, much to Yoda's disapproval and despite Yoda stating that the vision Luke had may not come true. Three months later - Luke returns to Dagobah (after rescuing Han Solo from Jabba the Hutt) to complete his Jedi training - but is devastated to discover that Yoda is dying. The loss is deep as he had not completed his Jedi training and more so due to how close he had become to the Jedi Master. Yoda reassures Luke that there is no need for more training and that he had learned all he needed to know.
He asks Yoda if he is now a Jedi Knight and Yoda states that he must first face Darth Vader - only then would he become a Jedi Knight - to which Luke states that he already had. Luke asks if Vader is his father and Yoda confirms this truth. Luke became angry that Yoda had known the whole time who his father was but had refrained from telling him yet forgave him at the moment of his death. Yoda tries to tell Luke about the existence of his twin sister (Leia Organa), but only states that there is another, and dies before he has the chance to finish his statement. Luke grieves over the death of his mentor and friend.
Yoda initially respected Palpatine for his clean slate. When Dooku revealed the existance of Darth Sidious and that hundreds of Senators were now under his control, Yoda accepted Sidious's existence, but dismissed the possibility that Sidious was controlling the Galactic Senate, stating that Dooku was a Sith Lord now and couldn't be trusted. When the CIS invaded Corosaunt, he began to suspect that Dooku was telling the truth. After the Execution of Order 66 and the Declaration of a New Order, Yoda learned that the now Emperor Palpatine and Darth Sidious were one and the same. Yoda vowed to kill the new Emperor, but failed.
Yoda trained Dooku as both a young boy and as his apprentice. The two became enemies after Dooku turned to the Dark side.
Yoda first met Anakin when Qui-Gon Jinn brought him to the Jedi Temple. Though he was sympathetic with the nine year old, he refused to allow Qui-Gon to train him due to the fear that he was vulnerable to the Dark side. Even after the Invasion of Naboo was lifted, Yoda was reluctant about Anakin being made Obi-Wan's apprentice, but agreed.
Over the years, Anakin came to highly respect Yoda, while Yoda gradually outgrew his mild fear of Anakin and came to have faith in him. However, Yoda was aware of Anakin's fear of loss and after promoting him to the rank of Jedi Knight, assigned him an apprentice of his own; Ahsoka Tano, as he believed that by becoming a teacher Anakin would mature emotionally and understand that his excessive bonding to those he cared about was unnecessary once Ahsoka would be ready to go off on her own.
Unfortunately, that plan backfired when Yoda and the rest of the Jedi High Council expelled Ahsoka from the Jedi Order and turned her over to the Republic for a crime she did not commit. Although Anakin ultimately succeeded in proving Ahsoka's innocence, she refused to rejoin the Jedi Order due to their lack of trust and support. The event shook Anakin's trust and respect for Yoda.
As the Clone War dragged on, Yoda secretly became wary of Anakin, sensing his fear of loss was increasing. Meanwhile, Anakin's faith in Yoda was further diminished when the latter denied him the rank of Jedi Master when Anakin was placed on the Jedi High Council, something Anakin perceived as an insult. Yoda also ordered him, via Obi-Wan, to spy on Palpatine, whom Anakin considered a friend and mentor, further fueling Anakin's anger.
When Anakin fall to the Dark side and became Darth Vader, Yoda firmly believed he was beyond redemption and ordered Obi-Wan to hunt down and kill him.
Yoda continue to believe that Vader was irredeemable and there was no good left in him, even as a Force spirit. However, this was disproved when Vader's son, Luke, was being tortured by Palpatine, and Vader broke away from the Dark side of the Force, becoming the good person he once was; proving that he was a lousy friend to Anakin in the end.