Phantom Ganon is Ganondorf's doppelganger in the Zelda series often appearing as a major boss.
The fight against him in Ocarina of Time was awesome. Such a nice end to the Forest Temple with him jumping painting to painting.
His appearance in Wind Waker got spooky, but I enjoyed the two battles against him.
His Four Swords Adventures appearance was forgettable.
I didn't even notice he was even in Twilight Princess. Though it was a cameo in one of Ganondorf's attack near the end.