This paper charts the relationship between Pompey the Great and Theophanes of Mytilene, and discusses the latter's role in the politics of the mid-first century BC, both in his hometown, where he was a distinguished local notable, and in Rome, where he was a valued advisor to Pompey, notably in the run-up to the Civil War. The historical work that Theophanes wrote on Pompey's achievements and the grant of Roman citizenship that he received from him have a prominent place in the discussion, which also explores the nature and function of the circles of advisors that surrounded some political leaders in the late Republican period.