Dido was a planet twice visited by the First Doctor — once before meeting Ian and Barbara, and once while travelling with them. On the first occasion, the population of the planet was tiny, less than one hundred individuals. On the second, the Doctor was pleased to have returned, noting the planet's friendly population.
In or soon after 2493, a human spacecraft crash-landed on the planet. The only survivors of the wreck were Vicki and Bennett, the latter a murderer who killed the other survivors and the natives of Dido, apart from two who survived. The First Doctor and his companions arrived on Dido in the TARDIS. They discovered the truth behind Bennett, and Bennett fell off a cliff while trying to run from the surviving Dido natives. The travellers took Vicki away in the TARDIS with them. (TV: The Rescue)