Martin Villiers is a member of the powerful Villiers Family, younger brother to Richard Villiers. He is the only sibling that has carried on the family business, and has very little part (other than familial support) in the machinations of both Fuchi and later Novatech. He has a competitive streak that prevents him from "falling in line" with his older brother, unlike Darren Villiers.
In System Failure, p 28, it refers to Richard Villers' "brothers Sam and Darren". This is probably a mistake, replacing Martin with Sam (as in, Samantha Villiers, Richard's ex-wife).