Princess Ruto

Princess Ruto (ルト) is a Zora introduced in Ocarina of Time. She's the daughter of King Zora, the king of the Hyrulean Sea Zoras, and attendant of Lord Jabu-Jabu, their patron deity. Her mother is suggested to have passed away some time ago. She's an only child, and described as wild, tomboyish and selfish. This does not mean that she neglects her responsibilities though. Ruto becomes the new Sage of Water after Link destroys Morpha.

Ocarina of Time
Ruto is the princess of the Zoras in Ocarina of Time. She's very independent and tends to solve problems on her own, often causing her father a lot of trouble. She is the keeper of the Spiritual Stone of Water, the Zora's Sapphire, which she was given by her mother. It is unclear how Ganondorf intended to get his hands on this Spiritual Stone, but the monsters infesting and influencing Lord Jabu-Jabu do seem to be his doing. When Ruto was attending Jabu-Jabu one day, he swallowed her along with his lunch. Ruto accidentally dropped the Zora's Sapphire inside Jabu-Jabu and lost it. Instead of getting help, Ruto went deeper inside Jabu-Jabu in order to get the stone herself.

Some time later, she may or may not have written a letter for help. The letter was found in a bottle in Lake Hylia and was signed "Ruto", but she denied knowledge of it. This letter at least is what brought Link on Ruto's trail. Ruto's disappearance had not been unnoted and the Zoras were looking for her. Link showed the letter he had found to Ruto's father, the King of the Zoras and guardian of the entrance to Zora's Fountain, where Jabu-Jabu resided. King Zora immediately granted Link access to Zora's Fountain so that he could go find Ruto. Link entered Jabu-Jabu the same way Ruto had done: getting swallowed while feeding the creature. He found her pretty quickly, but she refused to come with him, stating that she could care less about her father being worried, that she did not know anything about the letter and that she did not want Link's help. Link kept trying to convince her to either come with him or accept help, and eventually, she accepted his help. Link had to carry her around and could use her to keep switches down and kill enemies by throwing her at them. The duo managed to find the gem, but just as Ruto picked it up, the platform on which she stood was raised and she was separated from Link. Link went searching for her again, and ended up battling Barinade, which was infesting Jabu-Jabu's insides. After that, he and Ruto found each other again outside of Jabu-Jabu. Ruto confessed that she was quite impressed with Link's achievement and asked him what kind of reward he wanted. Link asked for the Spiritual Stone of Water. Ruto, having grown quite fond of Link, was happy to give it to him. When her mother gave her the stone, she had told Ruto that she should give it only to the man who will be her husband. Thus, after giving Link the Zora's Sapphire, she considered them engaged, even though Link did not understand what she was talking about.

Seven years later, evil returned to Zora's Domain and caused the complete area and it inhabitants to be frozen under a thick layer of ice. This fate also befell Ruto, but she was rescued by Sheik. She then went to the Water Temple in the hopes of finding a way to save her people. There is where she and Link met again. She was happy to see him, but was aware that was not the time to talk about love. Ruto asked Link to assist her in freeing the other Zoras and informed him on the workings of the Water Temple. After that, she headed off and Link did not see her again until he defeated Morpha. In the Temple of Light, Link learned that Ruto was the new Sage of Water. She told Link that she still loved him, but their engagement was no longer meant to be (due to her being a Sage), and he had to continue his search for Princess Zelda. Right before he left, she gave him the Water Medallion, and asked him to thank Sheik for saving her if he'd see him again.

When Link defeated Ganon, Ruto 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.

Ocarina of Time manga
Ruto seems to be far less tolerant of her father in the manga, ill concealing that she considers him annoying. She also says 'Zora' at the end of her sentences.

The Wind Waker
While Ruto did not appear in The Wind Waker, one of the stained glass windows in Hyrule Castle's basement depicted her.

Phantom Hourglass
In the Phantom Hourglass, one of the available treasure items is titled "Ruto Crown". The description states "Some say this regal crown was worn by a princess of Zora".

Trivia

 * Ruto, like several other characters from Ocarina of Time was named after a town featured in The Adventure of Link.
 * Ruto has a döppelganger in Majora's Mask named Lulu. Her model is slightly altered though: while Ruto did not wear any clothes, Lulu wears a dress.
 * Interestingly enough, if you throw Ruto in the water of Jabu-Jabu, she will fade away even though she is a Zora.
 * Medli from The Wind Waker has a role similar to Ruto's in the game, where Link must carry her around the Earth Temple, however, Medli is more useful since she has a "mirror" lyre and can be controlled by Link and has the ability to fly.
 * Whether or not this is directly related, Ganon kills the Sage of Water in an attempt to escape being executed in Twilight Princess.