Gear is basically what would result if you took that robot from The Iron Giant, removed his brains out, and replaced it with a faulty SIM card from a cheap Android knockoff from China.
As a random fansite once put it, Gear is childlike and seems to be quite a bit out of his mind (no wonder after being born a couple minutes before). Yet, he's aware of his heavenly powers, and is aware of how they can be misused.
Gear first appeared in the intro to the pilot ep, right after we Lazarus & the other evil-doers are seen chasing the heroes into Narnia.
His first appearance was in the adventure that took our heroes back to Jotho.