History
Humans, ruled by the governor, used the planet as a prison colony until the rare mineral Zeiton-7 was discovered there, prior to 2157. (PROSE: Lucifer Rising) The colonists were kept entertained by televised footage of various tortures and executions of the prisoners. The planet was really ruled by Sil, a Mentor who controlled the sales of Zeiton-7.
By the late 23rd century, the mining era of Varos, the voting population was 1,620,783, not counting the Governor and the Officers. The Sixth Doctor and Peri visited in this time when the TARDIS required Zeiton-7. (TV: Vengeance on Varos)