Sergeant Slab Rankle made his first and only debut in FBI Warning of Doom. He is a Mall Security official, and is not quite psychologically stable, as he takes his job way too seriously.

He keeps those who have broken the rules in an unescapable underground facility until they are eventually taken away to be turned into zombies. He has also installed countless lasers all over The City Center Mall and even resorts to releasing zombies to capture trespassers.

When Zim managed to get past his zombies to return a movie to the Video Outhouse, he tried to recruit him; however, Zim was uninterested in his offer and left the mall. It can be assumed Slab continues to guard the mall alone with his zombies.