Medli

Medli is a young Rito from The Wind Waker. She is the attendant of Valoo, the patron deity of the Rito. She's close friends with Prince Komali, whose grandmother Medli was the apprentice of. She's quite brave and responsible; Medli accompanies Link into two dungeons in order to fulfill her job as attendant of Valoo and as the Sage of Earth respectively. She's notable as one of the few characters the player could control other than Link.

The Wind Waker
Some time before The Wind Waker, Medli was chosen by Komali's grandmother to become her apprentice and successor as Valoo's attendant. Komali's grandmother had sensed what destiny had in store for the young girl, but kept quiet about it, instead using her position to teach Medli all that she had to know until the day fate would call her.

Eventually, Komali's grandmother died and Medli became the new attendant of Valoo. Everything went well, until Gohma appeared in the Dragon Roost Cavern and started tormenting Valoo. Valoo's home became inaccessible and Medli could no longer fullfill her job as his attendant. Shortly after, Link arrived on Dragon Roost Island and was asked to meet with Medli. Medli in turn asked him to meet her at the entrance of Dragon Roost Cavern after Link had spoken with Prince Komali. Link complied and told her about Prince Komali's behavior. Medli told link she felt partially to blame for it and asked him to help her get to Valoo. Link decided to help her and managed to get her to the entrance by following her advice.

Link followed Medli into the cavern a little later, only to find her locked up in a cage high atop the mountain and guarded by two Moblins. Link got rid of them and freed Medli, who informed him about what exactly turned out to be wrong with Valoo. She asked him save Valoo and gave him the Grappling Hook to help him reach Valoo. After this, Medli took off to get help from the other Rito.

Link, Medli and Komali met on the beach of Dragon Roost island a little later, when Link had saved Valoo from Gohma. Medli supported Komali in giving his most precious possession, Din's Pearl, to Link. As Link didn't understand ancient Hylian, Medli kindly translated Valoo's words of gratitude to Link. Coincidentally, she also gave Link her interpretation of Valoo's words, thus hinting where he should go next. They rather abruptly had to say goodbye when Komali ran away and Medli felt she needed to go with him.

After these events, Medli went back to studying for her job as Valoo's attendant, and she could often be found performing music on one of the cliffs of Dragon Roost Island. That's where Link found her when he returned to find the new Sage of Earth. Following Laruto's hints, he knew Medli was the new Sage due to her being the owner of the harp Laruto had been carrying as well. As instructed, he played the Earth God's Lyric for Medli in order to awaken her as a Sage. This caused Medli to faint and in her dream, she met Laruto. The two performed the Earth God's Lyric together. After this, Medli woke up again and asked Link to bring her to the Earth Temple.

Once at the Earth Temple, the King of Red Lions advised the two how to progress through the temple, resulting in one of the very rare times in a Zelda game that the player could control a character other than Link. The basic setup in the temple is that Medli closely follows Link unless she can't for whatever reason or because the player commands her to stay still. By pressing R, Link calls Medli to him. By using the Command Melody, the player gains control over Medli and can use her ability of flight to reach places otherwise inaccessible. Also, Medli can use her harp to change the direction of rays of light, which often is part of a more complex "light puzzle". Medli can also be used by Link to reach certain areas. Though Medli is not great at flying yet, she can carry Link across gaps for a short amount of time.

Link temporarily leaves Medli to fight Jalhalla, but she joins him again after that. Link conducted the Earth God's Lyric for Medli as she played the song on her harp. As they did, Laruto temporarily appeared next to Medli to play along. This restored some of the power of the Master Sword. Medli noticed this and urged Link to go to the Wind Temple. She would remain in the Earth Temple to assure the power to repel evil would stay in the Master Sword.

Medli appeared for the final time during the ending. Together with Tetra's crew, Aryll, Prince Komali and Makar, she picked up Link and Tetra after their battle with Ganondorf.

Trivia

 * Medli is known to appear in the upcoming Wii game Super Smash Bros. Brawl. As of now she is known to appear as a trophy, any other possible role is unknown at the time.
 * The symbol shown on her apron is similar to that of Nayru's Pearl.