I'm very, very fond of Sir Patrick Stewart OBE, and a few roles spring to mind.
Firstly, the old Tinker Tailor Soldier Spy. His scene with Alec Guiness is amazing. The interaction between the two is fierce, despite Stewart never saying a single word. It's all just watching his character think about what Guiness is telling him, and watching Guiness attempt what he knows from the start is an impossible task.
Next up, another excellent BBC drama. I, Claudius. He played the cold, ruthless, ambitious Power-behind-the-Throne Sejanus, and damn did he make a good villain. You watch him manipulate and dominate the various people in his life, and watch his enemies conspire against him for years, as he slowly picks them off, one by one.
Of course, all of Star Trek: TNG, but in particular these moments, where the show and the character really became powerful, emotional pieces that stick with you for years to come.
And, finally, his tremendous body of stage work. The list of great roles he has played in Shakespeare is too vast to go through here, but I think one of my all-time favourites will be his role as Claudius with David Tennant as Hamlet. As far as I'm concerned, it's one of the best versions ever made, right up there with Branagh's 4-hour epic.
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