Wendy Padbury, the lady who played Zoe Heriot during the time of the 2nd Doctor in Doctor Who, became a theatrical agent later? One of her clients is Matt Smith.
Also, at least according to the behind the scenes for ‘The Legend of the Cybermen’, she was Colin Baker’s agent as well. The more you know.
Janet Fielding, who played Tegan, became an acting agent and Paul McGann was her client when he got the role of the Eighth Doctor