The Iotians inhabit the planet Iotia. Externally, Iotians are humanoids that are physiologically identical to Humans, but internal differences exist between the two species.

In 2168, the Horizon visited the planet. During its survey mission, a member of the crew left behind a book, Chicago Mobs of the Twenties (referred to as "The Book"), which was discovered by the natives. The highly imitative Iotians reinvented their entire society based on "The Book", thinking it was the model for a perfect society.

In 2268, the USS Enterprise visited the star system for the second time and discovered the extent of the cultural contamination. After unusual negotiations with mob bosses on the surface, which required an intimidating show of force, Captain Kirk was able to create a loose system of government with the Federation as a "Godfather"-type figure. Doctor Leonard McCoy left behind his communicator so the Iotians may have been able to copy Federation technology.

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