Dr. Strangelove is a brilliant satire by Stanley Kubrick, It has an excellent story, excellent art direction and excellent cinematography.The acting is also brilliant but it is not the kind of traditional brilliance usually found in great acting.
Sellers is one of the few Oscar nominees to be nominated for more than one role, and he is the only one to be nominated for three roles in the same film. The best way to review his performance than is to take each part of his performance separately.
The first role you see him in the film is that of Group Captain Mandrake. Mandrake is a very particular character in the the film since he is not insane. Sellers perfectly plays Mandrake as the very proper RAF English Captain, who tries to learn the recall code from the crazed general Ripper. As Mandrake Sellers creates a satisfactory character who works very well in his scenes, and although he is not exactly going for laughs he helps create them through his restrained delivery. I really enjoyed how Mandrake always kept completely proper with all the insanity around him. Not an overly memorable character exactly but certainly fulfills his role exceedingly well.
The second role is that of the President of the United States Merkin Muffley. Sellers completely plays Merkin differently from Mandrake and creates completely separate characters. Merkin again does not seem totally insane but not really completely sane either. He plays Merkin equally well as Mandrake. Sellers characterizes Merkin very well as the not particularly confidant but concerned President of the United States. This time though Merkin is more in the position to create more laughs which Sellers does quite well. Many coming from his phone scene with the Russian leader. His president is incredibly memorable, and again he gives a perfect performance as Merkin.
His third and strangest role is Dr. Strangelove. This role really has no seriousness to its role, and Sellers handles the purely comedic role exceedingly well. Everything he does as Strangelove makes his scenes as memorable as they are. His mannerisms in this scene are perfect as is that very odd voice he used for this character. Strangelove could easily have fell flat and the movie really would have suffered but Sellers takes on the challenge succeeds fully. As Strangelove he again creates an unforgettable character who always creates many laughs. All three characters are created completely differently by Sellers. He plays each one exceedingly well, and gives a perfect performance for three different characters. His voices and mannerisms are all perfectly effective. Sellers succeeds with all three characters. Now they are all basically caricatures, but that does not matter for that is their purpose.