I remember when I read Walter, for example, six years ago now, I said, "This is the role for me." I said that to my family. There was something there that I knew was absolutely right, and that was just based on the character. That's when gut instinct comes into play. I know there are certain things I won't do.

I was a theater man, so I was never in the situation of being a handsome Hollywood leading man, and then having to age.

I find science really sexy and, at the time that I was a school kid, it certainly wasn't.

It was wonderful to be able to play a character who had so many colors and who was able to play comedy, to play incredibly vulnerable, which he did a lot of the time, to play the love story, and to play the relationship with the son, which is quite unusual. That's a gift to me, as an actor.

I loved playing Walternate because he was completely the same character, version 1985, and then it developed in such a different way, physically and mentally. So, to be able to play that, in the same television series, as playing the other ones was a fantastic gift for me.

My last two characters have been Denethor and Walter Bishop. Both will be hard acts to follow. That sits in the hands of my managers, at present. I just have no idea what's going to be offered to me.

Over the last 25 years, since a lot of science writing became accessible to layman, I've become quite a consumer of science. As a child, I wasn't streamed into science, and I regret that now.