Sil

Sil was one of the Mentors from Thoros Beta, and actively involved in various unethical business schemes.

As representative of the Galatron Mining Corporation on the planetoid Varos, Sil lied about the value of Zeiton-7 to get the cheapest price for it possible. He was also interested in buying and distributing recordings of the various tortures which passed for entertainment on Varos. These schemes ended when the Doctor informed the Governor of Varos of the true value of the commodity. He hoped to secure rights to videos of the torture of criminals on Varos (already served up on television as entertainment for Varos' oppressed citizens) and market them on other worlds (DW: Vengeance on Varos).

In 2379, on his homeworld of Thoros Beta, Sil became involved in weapons dealing with the primitive peoples of the planet Crontep. The Doctor's personality had changed meanwhile, to the extent that they worked together, the Doctor using his knowledge of future history to know the best investment prospects. While not explicitly stated, Sil was presumably killed by King Yrcanos in his rampage in Crozier's laboratory. (DW: Mindwarp)

Other possibly non-canonical information
Prior to 2379. Sil allied himself with the Ice Warriors to profit from their invasion of the planet Magnus, which he hoped to make have a colder climate, in order to suit the Ice Warriors, while he also made a profit selling the natives warm clothes (TME: Mission to Magnus).