In play Doctor Faustus, who was the intermediary of the Devil?

In Doctor Faustus, Marlowe retells the story of Faust, the doctor-turned-necromancer, who makes a pact with the devil in order to obtain knowledge and power. Both Doctor Faustus and Mephistopheles, who is the devil’s intermediary in the play, are subtly and powerfully portrayed. Source: https://www.britannica.com/topic/Doctor-Faustus-play