Like several previous novels in the Barsoom series, Synthetic Men introduces a completely new character as its protagonist: Vor Daj, a padwar (warrior) from Helium and a member of John Carter's personal guard. Vor Daj narrates the action in the first person, so that when John Carter appears in the story, he is described in the third person (unlike other Barsoomian novels that feature Carter as the first-person narrator). The novel also brings back a familiar character, Ras Thavas, the amoral mad scientist from the earlier novel The Master Mind of Mars.