Sil is one of the Mentors from the planet Thoros-Beta, a race of small half-humanoid, half-wormlike creatures with a ridge down the spine and a ruffle around the face. Some, more primitive, Mentors also have a sting at the base of their tail. The Mentors' main concern is finance; their culture is based around business, often illegal business, and turning a tidy profit. Sil, in particular, is a greedy little Mentor, and will do most anything for money. Sil initially worked as a delegate from the Galatron Mining Corporation, and on one assignment he travelled to the planet Varos to negotiate a yearly review of the market price for zeiton-7 ore. In reality, though, Sil's goal was to take control of Varos and thus own the only source for zeiton-7.
The downside to being a Mentor is that Sil and his fellow businessmen can never be far from water. As they do not often swim in their native seas, the next best thing is a portable water tank on which they are carried around by their bearers. Food is also an issue, and Sil likes to keep a supply of slimy green marsh minnows on hand. For translation purposes, Sil always wears a portable translator. Unfortunately, his language transposer has an "eccentric communication circuit", resulting in broken English - for example, in regard to the TARDIS, Sil proclaims "This mysterious most is!"
Sil is also a very selfish character. Whenever danger looms, his primary concern - in fact, practically his only concern - is his own personal safety, and he is quite vociferous about this fact. He was extremely concerned that a rival mining corporation, particularly Amorb, might steal the prospects of Varos away from him. Sil has a completely vicious, sadistic streak, and enjoys others' pain as entertainment. He also finds human females, particularly Peri, to be quite repugnant.
