Omega
Legendary Galifreyan explorer and scientist, and quite possibly first of the Time Lords alongside Rassilon (the jury’s still out on that one), Omega developed the technology required to power his and Rassilon’s time travel experiments, but got himself stuck inside a black hole or in a parallel dimension or something, having gone utterly bonkers, in the process.
Lord Buckethead attempts to bond with Doc’s molecules, but a surprise Colin Baker totally steals the show
The First and The Second join The Third on an adventure in an anti-matter universe for the Ten Year Anniversary of Doctor Who