Tash is the alien inventor in The Voyager Conspiracy who has built a catapult capable of hurling a ship across thousands of light years and who trades its use for Voyager's help in finishing it.
Tash appears in the sixth-season Voyager episode The Voyager Conspiracy. Stranded far from his own people after an accident with a wormhole, he has spent a long time constructing a catapult that uses a graviton surge to fling a vessel across enormous distances.
Voyager's crew help him repair the device in exchange for a turn once he has gone. Seven of Nine, overloaded with data she has been assimilating in her sleep, notices that the catapult runs on a tetryon reactor like the one in the Caretaker's array and spins a series of conspiracy theories around it, some of them casting Tash as an accomplice.
Her suspicions prove groundless. Tash launches safely and reports his arrival, and Voyager follows, cutting several years from its journey.