According to the late Ewen Green, 'Harold Macmillan was the most self-consciously intellectual Conservative leader of the twentieth century'. This chapter argues that there were two Macmillans, the pre-war intellectual, and the post-war opportunist. From this perspective, it is possible to understand his ambiguous contribution to the development of ideas within the Conservative Party. His most important work, The Middle Way, capped a series of volumes which were written either singly or in cooperation with others. The nickname 'Supermac', originally bestowed on Macmillan by the hostile cartoonist 'Vicky', ended up being regarded as a tribute to his preternatural political powers. In practice, probably the most important legacy of Macmillan's pre-war thought was the credence it gave to the argument that the post-war Conservative leadership had made a conscious accommodation with 'socialism', which amounted to a betrayal of the party.