Years ago, I read Don Widener's 1975 biography on Jack Lemmon and a quote from Widener, about Lemmon, has always stuck with me and has recently popped into my mind again, as I begin the development of Pasha Lebedyev.
For all his persona on screen, he was one of the saddest men I've known. You could see it in his eyes. The face would be laughing but his eyes were sad. I never found out why that was.
The highlighted line may be one of the keys to playing Pasha.