Hendrik Casimir (1909-2000), Dutch physicist. Casimir was born in the Hague and studied at Copenhagen, Denmark, and Leiden, Netherlands. In 1934 he introduced the theory of superconductivity called the 'two-fluid model', which was the basis of the BCS theory. However, he is best known for his prediction of the Casimir effect in 1948. Casimir suggested that two parallel conducting plates in a vacuum would experience an attractive force due to their influence on the electromagnetic vacuum. This force was detected in experiments carried out in 1958. Casimir recieved many honours, including Fellowship of the Royal Society.