GO-4 units are robots built by the BnL Corporation tasked with overseeing security aboard spacecraft, as well as handling miscellaneous other tasks. They're quite small, and easily recognizable due to the red police light atop their bodies.
A GO-4 unit served aboard the Axiom as the Captain B. McCrea's first mate, and assisted Auto with enacting Directive A-113, but was destroyed when he was knocked out of a window.