The first appearance of Ganon is in the original The Legend of Zelda for NES as the game's final boss. He basically has a simple story of a boar-monster who kidnaps the Hyalian Princess Zelda to obtain the power of the Triforce.
The final boss fight is pretty sweet. Ganon turns invisible for most of the battle which makes it rather shocking for an NES game. But he's not too difficult of a challenge to finish off for good. I felt a lot of pride finishing Ganon off since the game is an epic adventure to finish.
He does make a final appearance (in his original incarnation) in Zelda II: The Adventure of Link at the Game Over screen. The plot says if Link were to die, then Ganon's remaining followers would use the hero's remains to revive their deceased master. Kinda spooky.