I think Ron Moore knew from day one that his final Cylon surprise would be the emotional linchpin the show deserves. I could pick a hundred clues along the way to solidify my theory, but I will share the only clue that matters–and the only clue that proves it can’t be anyone but a being who has resided on Earth in the last fifty years:

“All Along the Watchtower”.

The musical trigger that reveals the “Four” in season three’s finale is the only intentional giveaway you need to acknowledge to draw an indisputable conclusion: Zak Adama is the final Cylon.

True, Moore said in an interview that Dylan doesn’t exist in the Battlestar universe, but he admitted the “idea” of Dylan existing to create verisimilitude with Earth–the one we all know and live on–does exist. No other character in the show would have any way of knowing this song unless he/she has LIVED ON EARTH recently.

Zak Adama is the only character in this show’s universe that could have been there (and still is there, I believe, drawing both races to him now), unless you make the rotten assumption that the final Cylon lives in the fleet, has been to Earth and knows the way there but just isn’t telling anyone. That is as lame as it gets. I think Moore and crew knew this all along.

Dying leader? Zak is likely president of the U.S or holds some other high office of power on Earth. And this will be the twist: Earth is not the salvation for the wandering humans and Cylons, the wanderers will be the salvation for Earth. Zak is not dying in the way Roslin is dying, ala some disease or injury. He's dying because Earth is dying along with all its inhabitants.

The Hybrid's message to Kara: "You are the harbinger of doom, Kara Thrace..." This only means that the Hybrid knows on some level that Earth is going to end and that by seeking Earth, the entire fleet and the remaining Cylons will die, too. This is a warning NOT to go to Earth.

The “Forgive me…I didn’t know” line from #3? She was the Cylon who ordered the kill on Zak when his ship failed in the days before the war, something Zak intended to have happen. We’ll learn this in the next couple of episodes and see it in flashback. I love this because it ties back to the very first episode of the original series AND fits beautifully with the current story. A Cylon would only say "forgive me" if he/she killed the Cylon once before. Nobody else on the show worth anything has "died" up to this point, and certainly not at the hands of D'Anna.

The Leobin line of “The final Cylon is Adama.” Not a lie. He just doesn’t know it is Zak and probably believes it to be Lee or Bill. Leobin doesn't lie, at least not in a blatent way like this...it would be terrible storytelling.

Starbuck’s visions? Do we really think she’s supernatural? No, Zak just transferred knowledge to her somehow when they were together. Kara is Zak's assurance that the survivors will find Earth before it is destroyed.

And finally, and this is the most important reason why it has to be Zak–there is NO emotional resonance with ANY other character. Will anyone CARE if it is Dualla? Really? Or Tom? Or Gaeta? Cally? Come on, who really would care in their guts and hearts if it is one of these minor characters who aren’t deeply tied to our main characters? Maybe Billy would achieve some emotional charge, but not even a sliver of what we’d get with Zak. Do you love Zak? No. Of course not. But you love the people who loved him. The emotional centers of the show are and always have been Bill Adama, Lee Adama and Starbuck, (ok, and Roslin, but now that she and Bill are in love...)

Only Zak will bring the emotions of the show to the peak it deserves. I think this is right and true from the emotional and logical angles. It all fits and nothing is cheated.

Now if only I can find proof that Rick Springfield once covered Dylan’s tune, the circle of proof would be complete…