The Pyrons were a warlike species from the planet Pyron. They attacked their neighbouring planet Vaga and wiped out the Vagans save for a few who left in an inter-dimensional craft. When the Fifth Doctor and Adric were detected on Vaga, the Pyrons sent a space-shark to destroy them. The Vagan ship returned and used a beta-force field to prematurely detonate the space-shark's warheads, destroying it. (PROSE: The Key of Vaga)