 The role of John Hart in Torchwood was written with the casting of Marsters in mind after he contacted the shows ' producers expressing his interest in appearing in the programme 's parent show , Doctor Who . The character is used to illuminate some of Jack 's own characteristics as a doppelgänger who provides both an exaggerated version of , and a parallel to , aspects of Jack 's persona . Both Marsters and the general media also compared aspects of Hart 's character to Marsters 's role as Spike in Buffy the Vampire Slayer and Angel . Whilst a few reviewers criticised the character in relation to his impact of the show 's tone , a larger number welcomed the character and the energy Marsters brought to the role . 
