Ollie is a member of Master Payne's Circus of Adventure. He's a mechanic who may or may not have the Spark. He first in the scene where Agatha establishes some credibility with master mechanic Rivet, and engages in a bit of one-upmanship himself.
His mechanical hand can be turned into (or replaced by?) a cannon.
In the novelization, this character is named Captain Otto Kadiiski. His diction is slightly different, as might be expected from a nonnative (Bulgarian, perhaps?) speaker.