The Tharils' were gifted with time sensitivity powerful enough to navigate a ship. Due to this sensitivity the only thing that could contain them was Dwarf star alloy. The Tharils could ride the Time winds. In appearance were almost completely covered in hair and all the males had long beards. They had slightly cat-like noses.
The Tharils once controlled a vast empire centred on the gateway. The gateway was a huge castle that stood on the boundary between N-Space and E-Space. The Tharils could pass between the two universes via gateways in the castle. Anyone else who passed through the gateway met a dead end. The Tharils enslaved various species including Humans. The Humans built robots called Gundans as the humans themselves were unable to approach the gateway. The Gundans attacked the Tharils and invaded the castle during the banquet for the kings.
As the Tharil Empire and dominion crumbled, the Human species began to exploit their former masters in a continuing cycle of oppression. The Tharils now became the slaves, used as forced navigators of the time winds and traded as rare and valuable commodities. Ships such as the Privateer under Rorvik which became moored in the Gateway were built of the dense Dwarf star alloy to prevent the Tharils escaping. When Rorvik’s privateer became stuck in the Gateway the Doctor and Romana befriended two Tharils, Biroc and Lazlo, and they explained the history of the Tharil race to them. The two Time Lords helped to free Tharils still trapped in the privateer. Romana stayed behind in the Gateway to help the Tharils build a new life based on freedom and equity.
By the time of the Novel Lungbarrow Romana, as President of Galifrey is in negotiations with the Tharils.