As far as Stargate : Atlantis goes they have wonderful casting and a great supply of recurring role actors. The one role that makes the show special in more ways than one is that of the hybrid wraith “Michael”.
Michael (Star Trek fans would know him as the regular cast member Commander Charles ‘Trip’ Tucker from Star Trek : Enterprise) is the name given by the residence of Atlantis to a wraith whom they capture and experiment upon by using a retro-virus created by Dr. Beckett.
The Wraith are part human but most descended from a human life sucking insect known as the Iratus bug. Hence the wraith feed on humans. Michael is injected with the virus and slowly his Wraith DNA is iradicated and he becomes mostly human and has no recollection of his past. The Atlantis team create a story about him being Lt. Michael Kenmore, a soldier assigned to Atlantis and who was attacked by the Wraith.
He must take the injections regularly or he will revert back to his Wraith form. When he finds out what the Atlantis team did to him, he is angry and escapes and thus becomes the nemesis of the team in Atlantis. He does help them when the Wraith reject him, calling him unclean, and feels betrayed and an outcast – not accepted by either humans or the Wraith. As a result one can feel sympathy towards him and understand his madness & anger.
Michael is killed in Season 5.