From Zelda Legends Wiki
Ganon is the main villain of the entire Legend of Zelda series. He is usually depicted as a gigantic blue pig, whose weapon of choice appears to be a trident. Ganon was revealed in Ocarina of Time to have once been human, a man who went by the name of Ganondorf. This human persona also appeared in The Wind Waker. He is the holder of the Triforce of Power and is usually nearly successful in his plots for the possession of the other two Triforce pieces.
The Legend of Zelda
In LoZ, Ganon was the final boss of the game, and appeared to be a monstrous blue pig. He attacked by turning invisible and firing magical fireballs at Link. Link could defeat him by hitting his invisible body with his sword and firing the Silver Arrows.
The Adventure of Link
Here, Ganon did not appear unless Link lost all of his lives. An ominous "Game Over" screen would appear followed by the text, "Return of Ganon," accompanied by an ominous voice-over of Ganon laughing.
A Link to the Past
In this game, Ganon masquerades as Agahnim, and is exposed by Link at the end of the game. When Link fights him inside the Dark Pyramid, Ganon summons his trademark silver trident and vicious fire bats to attack. Link can defeat him with the Silver Arrows.
At the end of Link's Awakening, one of the Wind Fish's nighmares manifests itself as Ganon. This Ganon wields a dual-bladed axe and fire bats. Link can defeat him with the Pegasus Boots or the Spin Attack.
Ocarina of Time
Here, Ganon is known as Ganondorf, the king of the Gerudo thieves. He obtains the Triforce of power, and is seemingly destroyed by Link in his human form at the end of the game. However, Ganon uses the power of the Triforce to transform himself into a demonic monster vaguely resembling his prototypical blue pig form. He is sealed away in the Sacred Realm at the end of the game.
After the player completes both Oracle games, the true villain of the story is revealed to be Ganon, who the witches Twinrova are attempting to raise from the dead using Princess Zelda as a sacrificial victim. After a battle with the witches, Link forces Twinrova to sacrifice themselves and faces off against a Ganon resembling the incarnations from LoZ and ALttP. This Ganon can fire spheres of dark magic at Link, cause small earthquakes, and reverse Link's directional controls to make the player confused and disoriented.
The Wind Waker
In the Wind Waker, Ganon is a human once again and schemes to raise the flooded Hyrule in order to rule it. He is thwarted by Link, Zelda, and the King of Hyrule. In the most indelible scene of the game, Link plunges the Master Sword into Ganon's head and turns him to stone.
Four Swords Adventures
In this game, Ganon uses his pawn Vaati in order to gain power in Hyrule. The four Links use the power of the Four Sword to defeat him and seal him within the Four Sword at the end of the game.
Ganon appears in both his beast and humanoid forms in Twilight Princess as the final boss. He instigated the spread of the twilight over Hyrule by negotiating with the usurper Twilight King Zant for freedom from his prison in exchange for new powers.
Ganon has failed to appear in only three games: Majora's Mask, Four Swords, and The Minish Cap.
Ganon's weapon of choice appears to be the trident, but in Ocarina of Time he wields dual swords, and in the original Legend of Zelda he uses no weapon and only attacks through magical fireballs.
Due to a mistranslation, Ganon's name was written GANNON in the original Legend of Zelda. This has led to a myriad of misspellings and fans often use the term GANNON-BANNED to point out such misspellings, as well as other misinterpretations of the series.
An explanation of the GANNON-BANNED usage and common misinterpretations of the series.