Malladus

Malladus, also known as the Demon King, is the name of the primary antagonist of Spirit Tracks. He is an immensely powerful demon that once terrorized the re-established land of Hyrule but was locked away beneath the altar of the Tower of Spirits by the Spirits of Good of the land after a prolonged war between them. In Spirit Tracks, the kingdom's chancellor, Cole, seeks to release Malladus from his prison and help him return to his former strength.

Background
A century prior to the events of Spirit Tracks, the land was peaceful and its people lived in prosperity, watched over and protected by the good spirits of the land. However, it was not long before an evil entity known as Malladus, or the Demon King, descended upon the land and began to wreak havoc upon those who occupied it. It soon became apparent that Malladus's strength was so immense that nobody seemed to be able to counter him, and he brought much ruin and devastation to the people in his conquest of the land. The land was cast into shadow and despair as he terrorized the people and caused great disruption for the good spirits. The Spirits of Good had no choice but to come down from the heavens and ensue in a long and bloody battle with him. Due to his sheer power and strength, it took the effort of all of the good spirits of the realm to equal Malladus's power and stand a fighting chance against him. Due to this, it soon became apparent that Malladus would not be easily vanquished, his powers being so strong. Not possessing the power necessary to truly kill the Demon King, the good spirits of the land could only subdue him since by that time their powers had been depleted greatly. They combined all of their efforts and exhausted all of their energies to drive Malladus deep into an underground prison. To seal this prison, they cast a series of shackles, what would eventually come to be known in time as the Spirit Tracks, across the land in four directions. To act as the lock on Malladus's prison, the good spirits created the great Tower of Spirits to mark where the Spirit Tracks converged. Thus, Malladus, the Demon King, was defeated, and peace once more reigned across the land. The good spirits, exhausted from the war, returned to the heavens, but not before giving the land over to the new settlers, who christened it as Hyrule and restored the ancient Hyrulean monarchy to govern the land following the great war with the Demon King.

Spirit Tracks
Malladus makes his debut in Spirit Tracks as an extremely powerful demon that once terrorized the land and its first settlers. Much of his background is told during the introduction, as well as the reason behind the Spirit Tracks and the Tower of Spirits, which act as the lock to Malladus's undeground prison, and as long as they remained intact, Malladus would be safely bound within.

Over a century later, Hyrule's Chancellor Cole concocts a scheme to free Malladus from his prison and unleash him upon the land once again. To do this, he causes large sections of the Spirit Tracks to begin to disappear, causing great alarm in the land's monarch, Princess Zelda. Zelda immediately suspects Cole due to his untrustworthy nature and decides to take matters into her own hands by investigating the Tower of Spirits herself without Cole's knowledge. Though she flees with her friend Link aboard a train to the Tower of Spirits, they crash along the way due to the tracks disappearing beneath them. They then witness the destruction of the Tower of Spirits, as it shatters into four segments that are swept away. Amidst the destruction, the Demon Train is released. It is at this moment that Chancellor Cole drops his guise and reveals himself to be a follower of Malladus, having Byrne incapacitate Link and Alfonzo, and stealing Zelda's body to use it as a vessel to restore Malladus to full power. This marks the beginning of a quest for Link to retrieve Zelda's body, restore the Tower of Spirits, revive Zelda completely, and ultimately stop the Malladus's return to power.

After Link and Zelda have cleared the Fire Temple, Malladus takes control of Zelda's body atop the Tower of Spirits. Byrne demands that Malladus give him a gift of power for his role in the recovery; however, Malladus only attacks him, knocking him out cold. As Malladus has not yet acclimated to his new body, though, this exertion is all that he can handle at the moment; he escapes with Cole on the Demon Train, retreating to the Dark Realm.

After retrieving the Bow of Light and the Compass of Light, Link, Zelda, Byrne, and Anjean travel to the Dark Realm to confront Malladus and Cole. Link manages to damage the Demon Train, allowing himself and Zelda to climb aboard atop it. There, Malladus completes his resurrection, taking total control of Zelda's body. Link and Zelda fight their way through Malladus and Cole's attacks to the front of the train, where Zelda seizes Malladus; Link then uses the Bow of Light to banish Malladus from Zelda's body. In the ensuing chaos, the Demon Train is destroyed, and all of them are thrown out of the Dark Realm.

Amidst the wreckage of the Demon Train, Malladus is forced out of Zelda's body. Zelda tries to reclaim her physical form, but finds that for some reason she can't; Malladus tries to repossess her, but he is stopped by Byrne, who gives Zelda the strength to reenter her body. As revenge, Malladus kills Byrne, to Cole's applause. At this point, Malladus possesses Cole instead, transforming him into an immense beast; Malladus is unable to maintain his hold on Cole's body for long, but as he says, he has enough time to reduce the world to ruin.

In the final battle, Zelda builds up her sacred power while Link protects her from Malladus's attacks. Once she is ready, she and Link use her power and the power of the Spirit Flute to weaken Malladus. Zelda takes the Bow of Light and has Link distract Malladus while she shoots arrows at his back; eventually, a ruby appears on his forehead. Link cuts off the two horns that protect the ruby before thrusting the Lokomo Sword through it; Zelda comes to his assistance, and together the two manage to shatter the ruby, killing both Cole and Malladus and returning peace to Hyrule.

Trivia

 * In the final battle, Malladus bears a strong resemblance to Ganon's Dark Beast form from Twilight Princess, as well the color scheme of his The Legend of Zelda appearance.
 * The Spanish-language version of Spirit Tracks refers to him as "Mallard", which is the name of the fastest steam-powered train ever built, and is also the derivative name for the English one.
 * Malladus is the second villain to possess Zelda's body, the first having been Ganondorf in Twilight Princess.
 * The song that plays as Malladus's Theme after you and Zelda finish the duet is a remix of the duet and the the song that plays when you travel be rails.