Regeneration in Doctor Who was a device created to explain the recasting of the main character, the Doctor himself. But it's something all Time Lords are capable of, and occasionally we've seen Time Lords other than the Doctor regenerate on-screen. E.g. the Master has regenerated once on-screen, and an unknown number of times off-screen. My question is:
how many regeneration events, other than the Doctor's, have appeared on-screen?
Main canon only (as far as such a thing exists in Doctor Who): the TV series, Old and New, plus the McGann film.