Midna

Midna is a character in the newest Zelda game, The Legend of Zelda: Twilight Princess. She is a resident of the Twilight Realm and a decendant of the ancient Twili people. At first she seems to be a strange, dark creature with an agenda of her own, but ends up rescuing Link, and can be seen later riding him in his wolf form while in the Twilight Realm.

Midna is one of the Twili, a race descended from wielders of powerful and evil magic who were banished to an alternate dimension by the goddesses Din, Farore, and Nayru. This alternate dimension, out of which the sublimated descendants could only exist as shadows, eventually became known as the Twilight Realm. She remains as an imp-like creature through most of the game. In recent time, the Twili have been converted to fearsome "shadow beasts" and Midna into an imp-like form by the self-styled Twilight King Zant. Midna reveals this information to Link in the Gerudo Desert.

At first, Midna is a "servant" of Zelda, proclaimed as the Twilight Princess. She finds Link, in wolf form, locked in a prison cell, and aids him in his escape. With this comes the new ability to talk to Midna whenever the player chooses, by pressing "up" on the directional pad. Even further along in the game, pressing "up" allows the player to choose from several of Midna's abilities, from teleporting via portals throughout Hyrule or transforming into Wolf Link on demand.

Midna can be compared to the likes of Navi,The King of Red Lions and Ezlo, in that she provides information throughout the game that serves to aid the player.

As she is turned to her imp form by Zant, it might be a homage to Majora's Mask in which Kafei is turned into his kid form by the antagonist.

After the Twilight Mirror is rebuilt, the Sages revealed much later in the game that Midna is the true Twilight Princess and ruler of the Twili race, not Zelda, who had previously been defined as the Twilight Princess by Midna herself, presumably to keep a cover on her identity. Zant, after usurping the throne from Midna, placed a curse on her that gave her the form she is in for most of the game. This curse could presumably not be lifted until Ganondorf, who Zant refers to as his god, is defeated.  After Link has faced Zant in battle, Midna uses the power to the Fused Shadows to destroy Zant (temporarily, as he could be revived by Ganon). She uses only a fraction of the power that the Fused Shadows hold to do this, and is utterly bewildered by their power. The Fused Shadow's power is also used to break the pyramid-shaped barrier around Hyrule Castle. Midna uses the power to transform into a giant, spider-like beast with a large pole-arm weapon (see below). This same form is used in an attempt to destroy Ganondorf during the ending sequences of the game, but the attack fails, and Ganondorf supposedly kills Midna, holding up the helmet part of the Fused Shadows that was Midna's trademark garment. 

After Link, with some assistance from Zelda, defeats Ganondorf once and for all, it turns out Midna survived and Ganondorf's spell on her was broken, allowing Midna to regain her true form. In a comical moment when Link first sees her true form, she is amused by his silence and asks, "Am I so beautiful that you've no words left?"

Before going back to the Twilight Realm, she bids everyone farewell and sheds a single tear, which is used to destroy the Twilight Mirror just after she returns to the Twilight Realm. She vows Link that she will "see [him] later," however this is highly unlikely as the Mirror was the last link to the Twilight Realm. As another last word, she asks that everyone "...remember that there is another world bound to this one." 