Lew Kowarski was a Russian born and naturalized French physicist. He was a lesser-known but important contributor to nuclear science. He participated in the British Tube Alloys on early nuclear weapon research. After the war he worked at CERN.

Tube Alloys was the research and development programme authorised by the United Kingdom, with participation from Canada, to develop nuclear weapons during the Second World War. Starting before the Manhattan Project in the United States, the British efforts were kept classified, and as such had to be referred to by code even within the highest circles of government.