>>213822014
He's just a very well written double crosser. The season 1 finale, the preds have a truce to deal with the aliens, the vok. Tarantulas betrays the truce. Turns out, not just to benefit the preds but also cause he does not like the Vok. It's all actually retroactive. The writers just realized Tarantulas doing all these things for greater purpose was more interesting.
You have to remember, the show was always really flexible. It was not Earth in season 1, the writers only committed to this in season 2, which if they didn't, would have meant no Ark ect. BW writers just found great ways to expand on most of the characters into season 2 and 3.