I have not seen Albert Finney's nor George C. Scott's portrayal of Scrooge, so I cannot say definitively that Alastair Sim 'owns' this role, but I sure have trouble imagining anyone topping him; he is superb, the nitpicking comments of TinMan-5 notwithstanding. This version will always have a special place in my affections, and I am glad to see I'm not alone in holding this opinion. In my view, this is the definitive film version of this venerable and beloved tale.
Review of A Christmas Carol
