Hinchcliffe explained some of the thinking behind the introduction of Leela. He wanted to create a Doctor-companion relationship similar to that between Eliza Doolittle and Professor Henry Higgins in the play Pygmalion.
Mat Irvine described how the carved face of the Fourth Doctor was created, with Tom Baker coming to the studio and being coated is plaster, while he had straws up his nose to allow him to breathe.
For the purposes of this list, a "DVD documentary" is one made especially for the Classic Series DVD range. For this reason, things like studio recordings, film trims/inserts and other documentaries featured on DVD releases are not included below.