Fred, as he was labelled by the Seventh Doctor, was the king of an alternate dimension traversed by the Sol Transit System.

Fred was the ruler of a "standalone dimension" separate from the universe and complete with its own laws of physics.

When the Sol Transit System was built, its utilisation of interstitial travelling techniques to traverse the dimensions inadvertently went too far, going off into uncharted territories, providing him with a pathway into its dimension. Fred tried to assimilate the Doctor's form and headset into its own but was devoured by Kadiatu Lethbridge-Stewart, who had taken on the shape of a black leopard. (PROSE: Transit)

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