Maximus is the Roman soldier assigned by Flavia to guard Pearl Forrester, Brain Guy, and Professor Bobo. Since the other guards confiscated Brain Guy's brain, the prisoners were unable to teleport and escape their impending execution. However, Maximus solved this (unintentionally) by giving Brain Guy his brain and casually asking if it was his, allowing the prisoners to escape. Right after this, Maximus is last seen arresting Flavia.
Behind the scenes
Although his name is mentioned when giving Pearl water (a Red Zone Cuba reference), he is credited on-screen only as "Roman Soldier".