 Lucas North is a main character in the seventh , eighth , and ninth series ; the ninth series reveals that Lucas " isn 't who you think he is . " Following the creation of the character by the show 's writers , Armitage was chosen early in the casting process , since the producers believed he could carry the mystery of the character . A tentative viewer of Spooks , he was approached for the role following the completion of the second series of Robin Hood , in which he portrayed series regular Sir Guy of Gisbourne . After agreeing to appear in Spooks , Armitage learned how to speak fluent Russian and lost a stone in weight in order to fit the description of his character . 
