Oh Gaeta: the poor guy had an amazing fall from grace. When the show begins, he dutifully serves aboard the Galactica and is heavily relied on by Adama. He was a friendly and hardworking man, but his growing association with Gaius Baltar would eventually be his undoing. Possessing a high intellect and having previously studied genetics, Gaeta was chosen to assist Baltar in the creation of a Cylon detector. The two men built a rapport which would lead to his role in Baltars presidential administration.
The administration is soon doomed to Cylon occupation. Gaeta anonymously aids the resistance, though hes deemed a traitor by those he helps. Gaetas aid is eventually revealed, thus saving him from execution. However, things would never be as they once were. He now saw the world differently and the loss of his leg, compounded by the suicide of Duala seemed to be the last straw. Gaeta had grown to despise the Cylons and was blinded by his hatred.
Gaetas union with Tom Zarek led to a brutal sequence of bloodshed. Through it all the tragedy of Gaetas nature remains: he is clearly a good man, but the world had poisoned his mind. Whereas Zarek had the Quorum mercilessly gunned down, Gaeta demanded a fair trial for Adama. This desire to be righteous went against what he was trying to achieve- thus dooming the coup to failure. If the Galactica crew showed a bit more gratitude for his sacrifices, perhaps he could have been saved.