Third in Marshal's book blogs is My Book, The Movie, in which authors have a go at casting actors for their characters (without the inconvenience of needing the actors to agree...).
It's surprising how difficult this can be! Each time I have a go at it, I come up with a different answer. It's not so much that the characters have changed, but that perception of the actors changes over even a few years. Though looking back on it, I find I've cast Russell Crowe for Pythax in The Pericles Commission, and then used him for King Pleistarchus in Sacred Games.
For Diotima I had Rachel Weisz in The Pericles Commission, my wife Helen as Diotima in The Ionia Sanction, and now with Sacred Games I think I might have hit on the perfect Diotima. I'm rather pleased with my idea for Nico too.