Throughout the Legend of Zelda series, Link often has a variety of partners accompanying him on his journey throughout the game. These partners usually provide helpful hints and and assistance with completing the game.
Epona is a horse sometimes owned by Link and sometimes by Lon Lon Ranch. She has had a number of appearances, but can only be ridden in-game in Ocarina of Time, Majora's Mask, Four Swords Adventures and Twilight Princess (however, in Four Swords Adventures, she can only be ridden for a short period of time). She appears in the Oracle games and The Minish Cap but is not a playable part of these games. She is Link's most faithful friend, and normally gets Link to other places at a faster pace than walking.
Navi is Link's fairy partner in Ocarina of Time. She joins Link at the start of the game at the request of the Great Deku Tree, and helps Link on his quest to defeat Ganon. She leaves for unknown reasons after the threat of Ganon has been lifted.
Tatl is Link's fairy partner in Majora's Mask. She was a companion of the Skull Kid, but he left her behind with Link after stealing Link's Ocarina. She then helps Link to defeat the cursed Majora's Mask and free Skull Kid of its influence. She stays with the Skull Kid at the end of the game.
Ricky, Dimitri, and Moosh are Link's three animal companions in the Oracle series. Each has a special ability that will aid Link on his quest: Ricky the kangaroo has powerful legs that allow him to jump onto high ledges in a single bound; Dimitri the Dodongo is a strong swimmer who can swim against strong currents and even up waterfalls; Moosh is a flying bear that can hover across pitfalls and large gaps. Though he encounters all three of them on his adventure, Link is eventually paired up with one in particular for the remainder of the game after receiving their flute, which allows Link to summon his chosen partner on command. The landscape of the LabrynnianNuun Highlands, and Natzu in Holodrum, changes to suit the abilities of the animal Link pairs up with.
Ezlo is a Minish wizard who was cursed by Vaati into the form of a hat with a bird's head. Ezlo helps Link travel through Hyrule and has the ability to shrink Link to Minish size. After Vaati's defeat, the curse is broken and Ezlo returns to the Minish homeland.
Midna, the Twilight Princess, is Link's partner in Twilight Princess. It is through her that Link can change into a wolf and back on will. She was cursed by Zant into an imp form, and she is restored to her original form when Ganondorf is defeated. In the end of the game she goes back to the Twilight Realm, and destroys the Mirror of Twilight. It is unknown if Link ever sees her again. Some fans theorized that there is a possible romance between Link and Midna.
Linebeck is a sailor who Link meets in Phantom Hourglass. He is greedy and loves treasure, but travels with Link after finding out he could have some gain from it. Linebeck is very cowardly. He stays at the shore while Link goes through dungeons and goes on islands, much like the King of Red Lions. At the end he puts aside his cowardice to try and help Link.
Ciela is Link's Fairy in Phantom Hourglass. She does not remember who she is, or where she came from. Regardless, she is more than happy to help Link in his quest to rescue Tetra from the Ghost Ship. She's good friends with Oshus, whom she affectionately calls "Grandpa". Throughout their adventure, she aids Link by providing helpful hints and information (not to mention keeping Linebeck's ego in check). Eventually, she learns that she is a one of the Ocean King's guardian spirits, the Spirit of Time and Courage, and in the climactic battle with Bellum, uses her newly-remembered powers to help Link stop time and win the day once again. At the very end, she stays behind with Oshus and the other spirits as Link returns to his own world. The other Servant Spirits can also serve as Link's companions.
Princess Zelda is the reccurring princess of Hyrule in Legend of Zelda series. In Spirit Tracks, Zelda accompanies Link in his quest to stop Chancellor Cole from releasing the Demon King from the Spirit Tower. When Zelda's spirit is separated from her body early on the game, Link is one of the few that can see her ghost and he helps her in retrieving her body. As a ghost, she has the ability to control Phantoms. It is theorized that there is a possible romance between Link and Princess Zelda, evident in several titles including Ocarina of Time, The Wind Waker, and Skyward Sword to name a few.
Fi is the ethereal spirit of the Goddess Sword, and is Link's companion on his journey in Skyward Sword. She has a synthetic voice similar to Midna, but unlike Midna is very factual, preferring to use percentages and numbers in her briefings to Link. She is a physical manifestation of the Goddess Sword, and resembles its hilt in her overall design. Fi was created by the Goddess Hylia to aid Link in his journey to save Zelda. She is programmed with knowledge of the land, as well as knowledge of enemies, and holds messages directly from Hylia to Link.
The Crimson Loftwing is a rare Loftwing owned by Link in Skyward Sword. He serves as Link's way of transport between the several Islands in The Sky and the several sections of The Surface, a role similar to that of Epona in many other games. Link and his Loftwing share a special connection; as a young boy, Link was able to ride his Loftwing without needing any instructions.