A robot assigned to Shunsaku Ban by Superintendent Notarlin to aid in his investigation. Amazed at the advanced technology of Metropolis, Shunsaku Ban often asks the robot questions to try and understand him a bit better. However, as robot protocol forbids him to have a human name, Shunsaku Ban addressed him as "Pero" instead of his more formal identification number 803-D-RP-DM-497-3-C.

(Source: Wikipedia)