Fefirhi Trikhobu was a Venusian mathematician. She was a member of the clan Poroghini, and the daughter of Dharkhig.
Barbara Wright became a good friend of Trikhobu during her short visit to Venus. After Barbara's abduction by the Sou(ou)shi, Trikhobu began working with the Doctor to help save her. To that end, she developed a mathematical formula that could be used to determine the spatio-temporal position of any living creature. The First Doctor used it to navigate the TARDIS to find Ian Chesterton after they were separated. (PROSE: Venusian Lullaby)