Fefirhi Trikhobu

 was a Venusian. She was a member of the clan Poroghini, and the daughter of Dharkhig. 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)