I was flicking through Doctor Who: The New Audio Adventures - The Inside Story (a guide to Big Finish's DW releases up to the 40th anniversary). In the artice for the Unbound story Sympathy for the Devil, it had an iterview with Sam Kisgart*, who played the Master.
I thought the Tennant part was quite portentious. And the Nick Courtney quip?
Mind you, the other answers are rather funny, too.
*an anagram to protect the famous. Go on, guess. No cheating.
Sam Kisgart said:What did you make of your Sympathy co-stars?
A young man called David Tennant - I think he'll go a long way. A very promising actor. With a very firm bottom. And Nick Courtney, of course - we were at ballet school together...
I thought the Tennant part was quite portentious. And the Nick Courtney quip?

*an anagram to protect the famous. Go on, guess. No cheating.
Last edited: