Peter Davison Doctor Who Actor Sarah Sutton Nyssa Actor Janet Fielding Tegan Jovanka Actor Leonard Sachs President Borusa Actor Elspet Gray Chancellor Thalia Actor Michael Gough Councillor Hedin Actor Paul Jerricho The Castellan Actor Max Harvey Cardinal Zorac Actor Colin Baker Commander Maxil Actor Ian Collier Omega , The Renegade Actor Neil Daglish Damon Actor John D. Collins Talor Actor Alastair G. Cumming Colin Frazer Actor Andrew Boxer Robin Stuart Actor Malcolm Harvey The Ergon Actor Ron Jones Director Johnny Byrne Writer John Nathan-Turner Producer