This is an English language adaptation of a book which was published in Welsh by the same author by UWP, Evan James Williams: Ffisegydd yr Atom. The book discusses his career – what he achieved along those he worked with and the places he worked, most importantly the Physics Department at Aberystwyth University – and outlines his scientific service during the war. It also looks at the man himself – his upbringing in a Welsh speaking home and community in Ceredigion - through the accounts given by those who knew him.