Baker played the part from 1984 to 1986. Prior to being cast as the
Doctor, Baker guest starred as Commander Maxil in the Peter Davison
story Arc of Infinity, the only actor to have done so prior to taking the role. The special begins with Colin Baker, lead writer and executive producer Steven Moffat, Sixth Doctor companions Nicola Bryant (Peri Brown) and Bonnie Langford
(Mel Bush), among others, examining the Sixth Doctor’s adventures and
discussing his famous foes, including the universe’s most slippery
business man, Sil.
The special also includes the Sixth Doctor story Vengeance on Varos,
in which the Doctor visits the planet Varos to obtain the rare ore
Zeiton-7, vital to the functioning of his TARDIS. But Varos is a
dangerous place, where rebels are tortured on live television and
executions are used to win votes from the public. Trapped in the dreaded
Punishment Dome, the Doctor and his companion Peri must fight for their
lives – and save the starving population from the machinations of the
villainous reptilian Sil.