Prometheus

Prometheus is the Titan of crafty counsel and forethought. He is known for giving humans fire. He is the son of Lapetus and Clymene.

History
Prometheus sided with the gods in the first war, because he knew that the Titans would lose, and as a result, he was not imprisoned. However, because of his meddling nature, he gave fire to humans, which boosted their progress as a species, and made Zeus angry. His punishment for giving humans fire was to be tied up, and have his liver eaten every day by a bird. Hercules saved him, and Prometheus was wary of the gods after that.

Later, he joined Kronos in the battle against the gods, and is given the responsibility of trying to get Percy to surrender. In that meeting, he gives Percy Pandora's Jar (pithos) and leaves. In battle he fought for Kronos, however, when the Titans lost, Prometheus claims he was merely pretending to be on Kronos' side as to minimize bloodshed. This possibly shows that Percy and Luke were able to defy his thinking, or alternatively, the indignity of being tied up and having his regrowing liver eaten by a vulture every day impaired his judgement of the gods.

A minor plot hole in The Sea of Monsters is that when Hermes mentioned someone "chained to a rock with his liver being eaten out" in the present tense, who is obviously Prometheus, despite the fact that he was rescued by Hercules centuries ago.