Theo Crosby RA (3 April 1925 – 12 September 1994) was an architect, editor, writer and sculptor, engaged with major developments in design across four decades. He was also an early vocal critic of modern urbanism. He is best remembered as a founding partner of the international design partnership Pentagram, and as architect for the reconstruction of Shakespeare's Globe in London. However, his role as éminence grise in British architecture and design from 1950 to 1990 helped effect much broader changes. Crosby's archive is located at the University of Brighton Design Archives.
Crosby studied architecture under Rex Martienssen, an acolyte of Le Corbusier, at Witwatersrand University Johannesburg. From 1944 he participated in the Allied invasion of Italy. His post-VE day travels around that country introduced him to a world—of urbanity and cultural generosity—which he had never experienced in South Africa, and which opened his eyes to the power of the public realm. He settled in England in 1948, following the South African government's official sanctioning of apartheid. In 1949 he began work at the modernist architectural practice of Fry, Drew and Partners on Gloucester Place in London, combining this with studying sculpture in the evenings at the Central School of Arts and Crafts. Here he came into contact with teachers Richard Hamilton, Eduardo Paolozzi and Edward Wright, with whom he would later work on the exhibition This is Tomorrow, and fellow students Alan Fletcher and Colin Forbes, with whom he would later form a design partnership. The Central, with its emphasis on cross-disciplinary work, would have a lasting effect on Crosby's view of the architect's role. He also formed links at this time with the modernist MARS Group, and the Architectural Association.