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 as a senior member of the Jedi Council, he was one of the few who dared question him, though he rarely did so.
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 were often at odds due to their differing beliefs; Yoda looked to 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 unorthodox ways, regarding them as "defiance".
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 be quite fond of Ahsoka and assigned her to be Anakin's apprentice.
However, when Ahsoka was accused of treason, Yoda, like most members of the Jedi High Council, 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. Nevertheless, he reluctantly conceded and had the young Togruta stripped of her rank and status as a Jedi.
Like many of the Jedi, Yoda was present during Ahsoka's military trial as presided over by Chancellor Palpatine and during Barriss Offee's confession, proving Ahsoka's innocence. He was surprised that Ahsoka had been innocent the entire time.
Along with the rest of the Jedi 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 anymore, Ahsoka refused reinstatement and left the Jedi Order for good, a decision that surprised all members of the Order, including Yoda.
Ahsoka's departure haunted Yoda for a long time 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.
He later warned Luke to not underestimate the Emperor.
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 Skywalker when Qui-Gon Jinn brought him before the Jedi High Council for testing. Although he was curious about the nine year old, Yoda did not share Qui-Gon's opinion of Anakin being the prophesied "Chosen One". He also sensed Anakin's emotional attachment to his mother and his fear of losing her. As Yoda considered such things to be dangerous, he thus deemed Anakin unfit for the life of a Jedi. Even after learning of Qui-Gon's death and Anakin's heroics during the Battle of Naboo, Yoda was against Anakin being made Obi-Wan's apprentice, but reluctantly agreed after Obi-Wan made it clear that he would train the boy with or without the Council's approval.
Over the years, Anakin came to highly respect Yoda, while Yoda gradually outgrew his 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 develop emotionally. He hoped that when the time came for Ahsoka to go off on her own, Anakin would understand that he need not be attached and feel so protective of those he loved.
Unfortunately, that plan backfired when Yoda, along with the rest of the Jedi Council, expelled Ahsoka from the Jedi Order and turned her over to the Republic military for a crime she did not commit. Although Anakin ultimately succeeded in proving Ahsoka's innocence, she refused to rejoin the 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 became increasingly wary of Anakin, sensing great turmoil within him. After experiencing visions of his secret wife dying in child birth, Anakin turned to Yoda for advice (albeit without telling him about Padme), but Yoda, unaware of the intensity of Anakin's love for Padme, said "train yourself to let go of everything you fear to lose". However, this only frustrated Anakin as he didn't understand what Yoda was trying to say. Not long afterwards, Anakin's faith in Yoda was further diminished when the latter denied him the rank of Master when Anakin was placed on the Jedi 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 fell to the Dark side and became Darth Vader, Yoda was saddened, but firmly believed he was beyond redemption and forgiveness, and ordered Obi-Wan to hunt down and kill him.
Even as a Force spirit, 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, becoming the good person he once was.