
The following constitute the principal cast, i.e. those with speaking parts.
The table shows how many speaking parts there are per episode; apparently Dalek Operator is on a par with a speaking part, even though they don’t speak! Roy Skelton voices most of the Daleks, and Michael Wisher does double-duty as a Dalek voice.
| Episode 1 | Episode 2 | Episode 3 | Episode 4 | Episode 5 | Episode 6 | |
| 1 |
The Doctor: Tom Baker |
The Doctor: Tom Baker |
The Doctor: Tom Baker |
The Doctor: Tom Baker |
The Doctor: Tom Baker |
The Doctor: Tom Baker |
| 2 |
Sarah Jane Smith: Elizabeth Sladen |
Sarah Jane Smith: Elizabeth Sladen |
Sarah Jane Smith: Elizabeth Sladen |
Sarah Jane Smith: Elizabeth Sladen |
Sarah Jane Smith: Elizabeth Sladen |
Sarah Jane Smith: Elizabeth Sladen |
| 3 |
Harry Sullivan: Ian Marter |
Harry Sullivan: Ian Marter |
Harry Sullivan: Ian Marter |
Harry Sullivan: Ian Marter |
Harry Sullivan: Ian Marter |
Harry Sullivan: Ian Marter |
| 4 |
Davros: Michael Wisher |
Davros: Michael Wisher |
Davros: Michael Wisher |
Davros: Michael Wisher |
Davros: Michael Wisher |
Davros: Michael Wisher |
| 5 |
Gharman: Dennis Chinnery |
Gharman: Dennis Chinnery |
Gharman: Dennis Chinnery |
Gharman: Dennis Chinnery |
Gharman: Dennis Chinnery |
Gharman: Dennis Chinnery |
| 6 |
Nyder: Peter Miles |
Nyder: Peter Miles |
Nyder: Peter Miles |
Nyder: Peter Miles |
Nyder: Peter Miles |
Nyder: Peter Miles |
| 7 |
Dalek Operator: John Scott Martin |
Dalek Operator: John Scott Martin |
Dalek Operator: John Scott Martin |
Dalek Operator: John Scott Martin |
Dalek Operator: John Scott Martin |
Dalek Operator: John Scott Martin |
| 8 |
Kaled Lieutenant: Richard Reeves |
Kaled Lieutenant: Richard Reeves |
Kavell: Tom Georgeson |
Kavell: Tom Georgeson |
Kavell: Tom Georgeson |
Kravos: Andrew Johns |
| 9 |
Time Lord: John Franklyn Robbins |
Severin: Stephen Yardley |
Severin: Stephen Yardley |
Severin: Stephen Yardley |
Severin: Stephen Yardley |
Severin: Stephen Yardley |
| 10 |
- | Gerrill: Jeremy Chandler |
Dalek Operator: Cy Town |
Dalek Operator: Cy Town |
Dalek Operator: Cy Town |
Dalek Operator: Cy Town |
| 11 |
- | Thal Soldier: Pat Gorman |
Dalek Operator: Keith Ashley |
Dalek Operator: Keith Ashley |
Dalek Operator: Keith Ashley |
Dalek Operator: Keith Ashley |
| 12 |
- | Ronson: James Garbutt |
Ronson: James Garbutt |
Ronson: James Garbutt |
Kaled Guard: Peter Mantle |
Thal Soldier: John Gleeson |
| 13 |
Ravon: Guy Siner |
Tane: Drew Wood |
Ravon: Guy Siner |
Bettan: Harriet Philpin |
Bettan: Harriet Philpin |
Bettan: Harriet Philpin |
| 14 |
- | - | Dalek Voice: Roy Skelton |
Dalek Voice: Roy Skelton |
Dalek Voice: Roy Skelton |
Dalek Voice: Roy Skelton |
| 15 |
- | - | Thal Politician: Michael Lynch |
Thal Politician: Michael Lynch |
- | - |
| 16 |
- | - | Mogran: Ivor Roberts |
- | - | - |
| 17 |
- | - | Thal Soldier: Hillary Minster |
- | - | - |
| 18 |
- | - | Thal Guard: Max Faulkner |
- | - | - |
There are an unusually high number of speaking parts in this story - more than The Sea Devils, for instance - and there seems to have been a limit of 14 per episode, which has been adhered to very tightly. For instance General Ravon isn’t in Episode Two, freeing a space for Tane, and Roy Skelton doesn’t voice the Dalek in Episode Two; that’s Michael Wisher.
Even though there are eighteen parts in Episode Three, this is compensated for by there being only ten in Episode One; Episode Two compensates for Episode Four in the same way.