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Horg was a member of the Tribe of Gum.
When the tribe's leader, Za, took too long to secure the secret of making fire from the First Doctor and his companions, Horg led the tribe in an uprising which Za's mate Hur tried, but failed, to prevent. Za emerged from the Cave of Skulls bearing a flaming torch given to him by Ian. Horg backed down and acknowledged Za as his leader. Horg was later among the tribe members who pursued the four strangers after their escape. He saw them enter the TARDIS, which vanished before their eyes. (TV: An Unearthly Child)