Chaos

Chaos was a concept, the opposite of order. It usually held a negative or evil connotation.

The Black Guardian represented chaos, and wanted to take control of the Key to Time so that chaos would "break across the universe," (TV: The Armageddon Factor) and later wanted to give enlightenment to the Eternals so that they would "invade Time itself, chaos would come again, and the universe [would] dissolve." (TV: Enlightenment) A later interface, however, would state that chaos also represented freedom and that too much law, which the White Guardian represented, could be bad. (AUDIO: The Destroyer of Delights)

The Mara was a spirit of chaos, which puzzled Nyssa as it created the Sumaran Empire, an empire implying order. (AUDIO: The Cradle of the Snake)

Megron was the High Lord of Chaos and Chief of the Carions, Lords of Chaos. He described Earth in the distant past as a "hot mass of chaos" and a "kingdom" of chaos. He became angry when the Fourth Doctor predicted that order would arise out of the chaos, which it eventually did. (AUDIO: Exploration Earth)