Lab Rat is the main antagonist of the Romero.exe series.
Lab Rat is a white mouse on two legs, with a large tail in the back and a light blue suit with orange buttons. He has blackish grey pants, a dark grey belt with a small gold buckle, and pink hands and feet. His most strange feature appearance wise, are his large white fangs that reside out of his mouth - these are said to have been formed by mutations the professor did to himself. He has a large blue collar below his mouth, held by another large orange button.
He is also shown to be very short out of his machine, even shorter than his rival: Romero.
Lab Rat is proud of his intellect, but also can be boastful of it. He's very sadistic and enjoys having things under his control. His obsessive attitude can lead him to his defeat, and his rivalry against Romero leads him to get upset, even throwing "tantrums". He's been described as insane or mad, as he tends to go all out with his plan - and plasters his face on every one of his creations.
- Despite the name, Lab Rat is said to be a white mouse.
- Lab Rat is also said to be an alias, his full name has of yet not been disclosed, however.