The Master

A version of the Master was a Time Lord from a parallel universe.

He used many fake names, including Roger, Peter, Geoffrey, Tony, Eric, Robert and Sam.

A parallel universe version of the Doctor mistook Bob for the Master and used Venusian aikido on him. (AUDIO: Exile)

Behind the scenes
Roger, Peter, Geoffrey, Tony, Eric, Robert and Sam all refer to the actors that played the Master, like Roger Delgado, Peter Pratt, Geoffrey Beevers, Anthony Ainley, Eric Roberts, and Sam Kisgart.