World-known physicist and cosmologist Dennis William Sciama died in Oxford, United Kingdom, on 18 December 1999. Since 1983, Sciama directed the astrophysics section of the Scuola Internazionale Superiore di Studi Avanzati (SISSA) in Trieste and served as co-organizer of many ICTP workshops and conferences. Sciama will be remembered for his provocative theories on the role of neutrinos in cosmology and for his many-universes hypothesis. He also was a brilliant lecturer and wrote several books for popular audiences, including The Unity of the Universe, The Physical Foundations of General Relativity and Modern Cosmology. His legacy will continue through the extraordinary number of students he taught and inspired at Cambridge, Oxford and Trieste, among them John Barrow, George Ellis and Stephen Hawking.