Impa

Impa is a character seen frequently throughout the The Legend of Zelda series. Typically, Impa is an older woman who serves the Royal Family of Hyrule. She always appears to know much about the legends and secrets entrusted to the Royal Family. Impa also serves as a nursemaid and/or bodyguard to Princess Zelda and often offers guidance to Link. While she was part of the story of the very first game and of its sequel, she did not appear within the canonic games until Ocarina of Time.

In both The Legend of Zelda and The Adventure of Link, Impa was depicted as a Hylian. That is, she has the characteristic pointy ears. However in Ocarina of Time, she was reintroduced as a Sheikah, one of the many races that made their first appearances in that same game. The typical traits of a Sheikah seem to be pointy ears and red eyes. These traits are also present in her Oracle games incarnation, implying that Impa also is a Sheikah. This new consistency and the relative small difference between a Sheikah and a Hylian opens the possibility that by retcon, the Impa of the first two games is a Sheikah as well. Of course, this does not have to be true, as several other recurring characters belonging to one of the human races have switched to a different one in certain incarnations, and the Impa from Ocarina of Time is not necessarily related to the ones from the first two games.

The Legend of Zelda
In both The Legend of Zelda and The Adventure of Link, Impa only appears in the game manuals. When Hyrule was under attack by Ganon's forces in The Legend of Zelda, Princess Zelda ordered her old nursemaid Impa to secretly flee and find the one who could save them. Ganon soon found out and sent his men after Impa. Though she managed to stay out of their reach for a long time, she was eventually captured. However, she was saved by a strange boy who managed to chase away Ganon's henchmen. Knowing that this was the one she had been looking for, Impa told him the whole story and asked him to go save Princess Zelda.

The Adventure of Link
In The Adventure of Link, several seasons passed since Ganon was defeated by Link in The Legend of Zelda and Impa had resumed her normal duties. One day, Link came to her because he worries about a strange mark that had appeared on his hand. When Impa saw the mark, she was initially startled, but quickly regained her composure. She then took Link to a door in North Castle that only the members of her family knew how to open. In the room behind the door lay a princess of Hyrule from ancient times and before Link could ask any questions, Impa told the princess' story. When she was done telling, she picked up six crystals and a scroll lying on a stand next to the altar and gave them to Link. She explained that these items were handed down in her family for generations while waiting for the one who was chosen by destiny to save the princess. She implored Link to follow his destiny and save the princess, to which he agreed.

Ocarina of Time
In Ocarina of Time, Impa was born and raised in Kakariko Village, the village of the Sheikah. She was selected as Princess Zelda's attendant and likely left her village around that time, giving it to the people of other races. Though Hyrule Castle became her new home, she still kept a watching eye over Kakariko though, but most of her attention went to the young princess. Until Link came along, Impa was the only one who believed her visions.

Link met Impa for the first time in Hyrule Castle, where she taught him Zelda's Lullaby. She then helped him leave the castle. Outside, she advised Link to head to Death Mountain to find the next Spiritual Stone and returned to the princess. Unfortunately, while Link was searching for the remaining Spiritual Stones, Ganondorf attacked Hyrule Castle. Impa took Princess Zelda and fled the castle with her. She only barely managed to escape Ganondorf and stayed into hiding with the princess for seven years. It is likely that she was the one who raised Zelda during those years and taught her what she had to know to pass off as a Sheikah. Impa also kept protecting Kakariko Village to her best effort.

When Zelda was old enough to take care of herself, Impa started focusing on her old village again. An old evil that had plagued Kakariko Village in the past and that was locked up by Impa, had returned. Impa went to the Shadow Temple in order to lock the creature up again. When Link went to Kakariko Village after his seven year slumber, Sheik greeted him and told him about Impa. Link followed Impa into the Shadow Temple and was able to kill the creature, awakening Impa as the Sage of Shadows. As her new duty as a Sage prevented her from being at Princess Zelda's side, her final words to Link were a request to protect the princess on her behalf. Before leaving, Link received the Shadow Medallion from her.

When Link defeated Ganon, Impa and the other Sages bundled their powers to seal away Ganon. During the ending, she could be seen overlooking a celebrating Hyrule on Death Mountain with the other Sages.

Oracle of Ages and Oracle of Seasons
Impa is the trusted nursemaid of Princess Zelda in Oracle of Ages. Impa, sent by Zelda to bring Nayru back to Hyrule for protection, meets Link when she finds she cannot move a large rock with the Mark of the Hero upon it: Link moves this with ease. However, Veran, Sorceress of Shadow, had possessed Impa. Veran transfers herself into Nayru, leaving Impa's body. After Nayru is kidnapped, she puts all her trust in Link to save Labrynna.

Impa is the trusted nursemaid of Princess Zelda in Oracle of Seasons, and she has been sent to bring the Oracle of Seasons away from the dangers that threaten her in Holodrum, and take her back to Hyrule. After Din is captured by Onox, she puts all her trust into Link, as he bears the mark of a Hylian hero.

The Wind Waker
While Impa doesn't appear in The Wind Waker, one of the stained glass windows in Hyrule Castle's basement depicts her Ocarina of Time incarnation, along with the other sages from Ocarina of Time.

The Legend of Zelda comic
Impa's appearance in the Legend of Zelda comic is very similar to that of her The Legend of Zelda and The Adventure of Link depiction, and she only briefly appears in three stories out of the twelve featured in the comic, including He Also Serves, Day of the Triforce, and Choices.. She is Princess Zelda's nursemaid and is wise in all things concerning the land of Hyrule and the Triforce. Because of this, her advice to Link and Zelda is crucial in their quest to protect the kingdom from Ganon. In He Also Serves, Impa is the one that warns Link, through the prophetic words of the  Triforce of Wisdom, that Hyrule could fall at the hands of Ganon if the  young hero leaves the North Palace to accompany the princess to another town in the kingdom. She also explains to Zelda that the Triforce of Wisdom cannot be used as a weapon, but instead as guidance to be able to wield the sacred Silver Arrow. When Zelda goes to Impa and worriedly tells her that the Triforce of Wisdom has disappeared, Impa explains to her that it is because the Day of the Triforce has arrived, which causes all three Triforce pieces to disappear for one day every decade.

The Shadow Prince
In The Shadow Prince, Impa appears once again serving as Princess Zelda's nursemaid, portrayed as an elderly woman. She plays a major role in the book since it is through her wise words that Link is able to discover Charles's true identity. She is first introduced in the book when Link and Charles are having the archery match. Just as Link is choosing the arrow that he will use for the match, Impa walks towards him and tells him to use the Green Arrow that she puts in his hand, saying it is enchanted with magic. After the Green Arrow lands way off the bulls-eye, Impa warns the young hero that Charles is in possession of strong magic.

Throughout the book, Link often goes to Impa for advice to consult about his next step. At one point, Impa suggests to him that he should have patience and not defy Charles before he learns of his true identity. She then sends him off to the Water Town of Saria to retrieve the Mirror of Truth and gives the young hero the Golden Whistle in case he may need it, the former being the item that will ultimately help lead to Charles's defeat.

Oracle of Ages manga
In the Oracle of Ages manga, Impa is shown to possess almost superhuman strength, being able to carry a cow over her head with relative ease, despite it annoying her greatly.

Trivia

 * In Twilight Princess, the character Impaz is a reference to Impa from Ocarina of Time and an implied descendant.