A Frogstar Scout robot is a robot that was sent out from the Frogstar to search for Zaphod Beeblebrox, eventually taking him and the whole building he was inside (the Hitchhiker's Guide offices) back to the Frogstar. There are four known classes: A, B, C, and D, which were identified for Zaphod by Roosta, an editor for the Guide. They first appeared in the Secondary Phase of the original radio series.
Frogstar Scout robot Class A
The Frogstar Scout robot Class A is described as a "small black spiderlike object." It can fly and was sent out to search for Zaphod.
Frogstar Scout robot Class B
The Frogstar Scout robot Class B is described as a "larger black spiderlike object" (in comparison to Class A). It was sent out to search for Zaphod.
Frogstar Scout robot Class C
The Frogstar Scout robot Class C is undescribed. It can fly and was sent out to search for Zaphod.
Frogstar Scout robot Class D
The Frogstar Scout robot Class D is described as a "gigantic black shape...the size and shape of a tank" and is armed with an electron ram (a weapon described as a "sharp prong which spat a single lethal blaze of light...a wall roared and collapsed as a heap of dust"). It was sent out to search for Zaphod, who ordered Marvin to fight it so he could escape.
Marvin tricked the tank into guessing what he was armed with, and when Marvin eventually revealed he had nothing, it made the tank so angry at the thought that Marvin's master would be so heartless to leave him here undefended that it smashed through the walls and ceiling using its electron ram. It then smashed through the floor, but as the floor happened to be the fifteenth, it fell and was destroyed from the impact. Marvin then proceeded to remark "What a depressingly stupid machine," and started to catch up with Zaphod.