Friedrich Wilhelm Strassmann (German: [fʁɪt͡s ˈʃtʁasˌman] ^ⓘ; 22 February 1902 – 22 April 1980) was a German chemist who, with Otto Hahn in December 1938, identified the element barium as a product of the bombardment of uranium with neutrons. Their observation was the key piece of evidence necessary to identify the previously unknown phenomenon of nuclear fission, as was subsequently recognized and published by Lise Meitner and Robert Frisch.

In their second publication on nuclear fission in February 1939, Strassmann and Hahn predicted the existence and liberation of additional neutrons during the fission process, opening up the possibility of a nuclear chain reaction.

Friedrich Wilhelm (Fritz) Strassmann was born in Boppard, Germany, to Richard Strassmann and Julie Strassmann (née Bernsmann). He was the youngest of nine children. Growing up in Düsseldorf, he developed an interest in chemistry at a young age and conducted chemistry experiments in his parents' home. His family was of modest means, and his father died at a young age, worsening the family's financial situation. Financial considerations limited Strassmann's initial choices of where to pursue his higher education and what subjects they should be.

Strassmann began his formal chemistry studies in 1920 at the Technical University of Hannover, supporting himself financially by working as a tutor for other students. He received a diploma in chemical engineering in 1924, and his PhD in physical chemistry in 1929. His doctoral research was on the solubility and reactivity of iodine in carbonic acid in the gas phase, which gave him experience in analytical chemistry. Strassmann's doctoral advisor was Hermann Braune [de].

Subsequently, Strassmann received a partial scholarship to the Kaiser Wilhelm Institute for Chemistry in Berlin-Dahlem, beginning in 1929. There he studied radiochemistry with Otto Hahn, who arranged twice for his scholarship to be renewed. When his scholarship expired in September 1932, Strassmann continued to work as a research student in Hahn's laboratory, without a stipend but without having to pay tuition.

In 1933 Strassmann resigned from the Society of German Chemists when it became part of a Nazi-controlled public corporation. He was blacklisted by the Nazi regime. As a result, he could not work in the chemical industry nor could he receive his habilitation, as required to be an independent researcher in Germany at the time. Lise Meitner encouraged Otto Hahn to find an assistantship for Strassmann at half pay, and he eventually became a special assistant to Meitner and Hahn. Strassmann considered himself fortunate, for "despite my affinity for chemistry, I value my personal freedom so highly that to preserve it I would break stones for a living."

Strassman's wife Maria supported his refusal to join the Nazi Party. During World War II they concealed a Jewish woman, musician Andrea Wolfenstein, in their apartment for months, putting themselves and their three-year-old son at risk especially considering the housekeeper and downstairs neighbors were Nazi supporters.

Strassmann continued his research in radiochemistry during World War II, although he did not work on weapons development. He disdained the Nazi regime and is reported to have said, "If my work would lead to Hitler having an atomic bomb I would kill myself."