Sil Sil was a Mentor from Thoros Beta . He was actively involved in various unethical business schemes during the 21st , 23rd , and 24th centuries . Biography . As representative of the Galatron Mining Corporation on the planet Varos , Sil lied about the value of Zeiton - 7 to get the cheapest price for it . He was also interested in buying and distributing recordings of the various tortures which passed for entertainment on Varos . These schemes ended when the Sixth Doctor informed the Governor of Varos of the true value of the commodity . Sil 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 . ( TV : " Vengeance on Varos " ) Prior to 2379 , Sil allied himself with the Ice Warrior s to profit from their invasion of the planet Magnus , which he hoped to make have a colder climate to suit the Ice Warriors , while he also made a profit selling the natives warm clothes . ( AUDIO : " Mission to Magnus " ) In 2379 , on his homeworld of Thoros Beta , Sil became involved in weapons dealing with the primitive peoples of the planet Krontep . The Sixth Doctor , seemingly as a ruse , worked together with Sil , the Doctor using his knowledge of future history to determine the best investment prospects . ( TV : " Mindwarp " ) In 2382 , The Universal Monetary Fund sent Sil to London to try an recuperate some of the money they had lent Amadeus Boscoe ' s government . He suggest radical cuts to aid this recuperation and asked his master Lord Mav for a further loan . Boscoe allowed him to become part of his government . He used Anzor ' s TARDIS to lure the Sixth Doctor to London , where he asked Cordelia Crozier to experiment on him to find all immunities . He suggested releasing Cholera and the Bubonic plague to reduce the population of United Kingdom . He killed Crozier , because of the death of Kiv and led Cordelia to believe the Doctor did it . ( AUDIO : " Antidote to Oblivion " ) At some point , Sil was present on Earth in the 21st century , where he entered the profession of TV programming . Sil planned to bring torture to the modern age , by putting undesirable humans in a house and psychologically pitting them against each other . The Tenth Doctor learned of this thanks to a magazine , " Yikes Mag " , owned by Rose Tyler and planned to stop him . However , when confronting Sil , Rose quickly pointed out that his pitched TV series had already been done , which , much to the Doctor ' s shock , lead to the two bonding over a shared morbid fascination with the " torture " committed to guests on reality TV . ( COMIC : " Untitled " ) Personality . Sil seemed to be sadistic and contemptuous of humanoid life - forms , once stating that " There is nothing I more enjoy than human suffering . " ( TV : " Mindwarp " ) He was extremely self - centred , greedy and manipulative - as shown in his attempt to govern Varos - as well as hot - tempered and impatient , being given to temper tantrums when things did not go his way . He even screamed at people when they did not respond to his questions immediately . ( TV : " Vengeance on Varos " ) Habits and quirks . Sil liked to eat marsh minnow s . ( TV : " Mindwarp " , AUDIO : " Antidote to Oblivion " ) Appearance and behaviour . Like all Mentors , Sil looked like a slug with humanoid features and fin like appendages on his head and in between his arms and torso . ( TV : " Vengeance on Varos " ) His skin tone varied between dark brown ( TV : " Vengeance on Varos " ) and light green . ( TV : " Mindwarp " )