Alan Turing
Jeff Attwood has a post on possibily the greatest man in the computing age, Alan Turing. As Jeff states during WW2 Alan helped break the enigma code and went on to become one of the fore-fathers of AI. There are several books on Alans life that are well worth reading with the Andrew Hodges book one of the best.
Alan is one of my personal heros, some of Alans greatest work in computing occured here in Manchester, the place I was born and grew up in. After the war Alan conducted research into computing and maths at the University of Manchester. He worked on one of the first computers ever built the Manchester Mark 1 as well as conducting a great deal of his AI and machine learning research there. The memorial you see above was built in his honor and rightly so, with out him I cannot imagine what the world may have become.