The Master

In a parallel universe, the Master was a Time Lord.

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 actors that played the Master: Roger Delgado, Peter Pratt, Geoffrey Beevers, Anthony Ainley, Eric Roberts, and Sam Kisgart.