To kick things off, here's a look at the great Geoffrey Palmer in the three roles he played on the series (none of whom had a happy ending).
Could they have been related in any way? Perhaps they all shared the same soul. As we thought we learned from the Minbari and the humans, reincarnation spans the galaxy. (Of course, for the Minbari it was a combination of mistaken identity and time travel when it came to Sinclair and Valen sharing the same soul.)
But since 'Doctor Who' spans the vast timeline of the TV Universe, I don't think there's any fear that any of these three characters existed at the same time. And as always, I could be wrong about that.....