Well first off the Calliach were powerfull to the extreme with the use of magic, and the Watcher is still 3rd most powerfull ever. And you never see a trow in the watcher's army, and the Trow 'obliterated' the Calliach. Also, the watcher is about twice as large as a zerk, so he is probabally a giant. Also, he is very, very, very old. This gives me reason to beleive he was a Calliach.
Note- The Deceiver, ally of the trow was the arch enemy of the watcher... perhaps The Deceiver helped the Trow obliterate the Calliach before Moagim was even heard of, and The Watcher hates The Deceiver with a passion for doing that.
This also goes with him faking his death and the deceiver faking his theory (the deceiver faking his is mine ;))
We know The Watcher is several millenia old. He was already feared by Mazzarin (read the tfl Thrall flavor), one of the most powerful avatara, they think of him as a devil from an unkown time terrorizing the light.
I'd once again like to point out his size and ability with magic :) showing he's not human.
