Colin (a.k.a. part #223219B) is a small, round, melon-sized, flying security robot which Ford Prefect enslaves to aid in his escape from the newly re-organized Guide offices in the novel Mostly Harmless. "Its motion sensors are the usual Sirius Cybernetics garbage." Ford captures Colin by trapping the robot with his towel and re-wiring the robot's pleasure circuits, inducing a cyber-ecstasy trip.
Ford uses Colin's cheerfulness to break into the Guide's corporate accounting software in order to plant a Trojan Horse module that will automatically pay anything billed to his InfiniDim Enterprises credit card. Colin also saves Ford's life when the Guide's new security force, the Vogons, fire at him with a rocket launcher after Ford feels the need to jump out of the window. Colin was last seen being sent (at the risk of possible lonely incineration) to look after the delivery of the Guide Mark II to Arthur Dent in the Vogon's postal system.
Colin was named after a dog which belonged to a girl, Emily Saunders, of whom Ford had fond memories. Colin appears in the novel Mostly Harmless, and in the radio series he was played by Andrew Secombe.