The Democratic Underground was a secret organization on Terminus, originally created by secretive democratic elements of the First Foundation as an opposition to Mayor Indbur I in 214 FE. His reign was growing more and more tyrannical and they hoped to resist his dictatorship for the good of the Seldon Plan.

The need outlasted during the reign of his successors, Mayors Indbur II and Indbur III. When the Mule took over Terminus from Indbur III and the Foundation fell in 295 FE, the Democratic Underground adjusted their plans to overthrowing the Mule's control and became the leading organization in the resistance against the occupation. The organization operated as a regular political party until it was driven into hiding by the new conditions, and its members terrorized.

A plan to assassinate the Mule was arranged in early 296 FE. The assassin was supposed to be Captain Han Pritcher but it failed and no further attempts to kill the dictator were made. He died ten years later in 306 FE and the membership of Terminus in the Union of Worlds ceased.

The Democratic Underground eventually faded out and merged with Terminus agents of the Second Foundation.