Sam Fisher (played by William Mapother) is the kind of man for whom psychological terms are inadequate, displaying as he does practically every negative trait of both a sociopath and a psychopath. He is a brutal criminal who takes what little pleasure he gets from life in ripping things away from others, from possessions to life itself.
John Gray was his inside man on numerous jobs, until the younger man met Emily and decided he'd done more than enough harm in the world. John set up his former allies by working with law enforcement, but Sam never spent much time in prison, escaping and, in "Sanctuary", coming to hunt down his betrayer. Sam, however, didn't count on the bravery of the monks, particularly Abbot Stevens, and the interference of Christopher Chance and his crew. He is shot dead by John himself whilst trying to kill 'the stooge' as slowly and painfully as possible, which has a certain karmic symmetry.