Based on the Pulitzer Prize winning novel by Viet Thanh Nguyen.
Robert Downey Jr. said filming this series was a welcome contrast to his role in Oppenheimer (2023): "I knew that playing Strauss, in 'Oppenheimer,' was going to be like picking fly shit out of pepper - that it was going to be extremely exacting, that it was going to be... not confining, but liberating by its varied implicit limitations of what my usual toolbox is. So I had a feeling that, like a coiled spring, 'Sympathizer' would be my unwind."
When asked why he didn't direct the whole seven-episode-miniseries and only the first three episodes, Park Chan-wook answered that his experience on The Little Drummer Girl (2018), in which he directed all six episodes, was so demanding that he didn't think he could do the seven, so he focused on setting the look with the first three and then passing the job to other directors while he focused on the scripts.
Park Chan-wook suggested Robert Downey Jr. to play the American antagonist figures Claude, Professor Hammer, Ned Godwin and Niko Damianos.