Leonard (Leon) Sternbach (born 7 May 1908 in Abbazia, now Opatija, Croatia, died 28 September 2005 in Chapel Hill, North Carolina, USA) was an eminent chemist who gained international fame for his synthesis of chlordiazepoxide, the first of a series of benzodiazepine drugs that revolutionised the treatment of anxiety and other psychiatric disorders.

Sternbach, who came from a Polish family, graduated from the Jagiellonian University in Krakow, where he gained a solid grounding in chemistry. He obtained a master's degree in pharmacy (1929), followed by a doctor of philosophy in chemistry (1931). He worked at the Jagiellonian University and then went to Vienna and Zurich on a scholarship. Due to increasing political tensions in Europe and as a Jewish person, Sternbach decided to emigrate to the United States, where he continued his scientific work.

In 1940, Sternbach joined the US branch of the pharmaceutical company Hoffmann-La Roche, where he spent the rest of his career. His research focused on the synthesis of new chemical compounds that could be used in medicine. In the 1950s, while researching chemical compounds capable of combating mental illness, Sternbach discovered a series of compounds that later became known as benzodiazepines. The first drug discovered from this group was chlordiazepoxide (Librium), launched in 1960. This was soon followed by the introduction of diazepam (Valium) in 1963, which quickly became one of the most prescribed drugs in the world.

Sternbach is recognised as one of the most influential chemists of the 20th century due to his groundbreaking discoveries in the field of psychiatry. His work on benzodiazepines changed the face of anxiety disorder treatment, introducing more effective and safer therapeutic options than the previously available barbiturates.

Leon Sternbach received many awards and honours for his scientific achievements, including the prestigious Albert Lasker Award for clinical medical research. His work had a far-reaching impact not only on chemical and pharmaceutical science, but also on the lives of millions of patients worldwide.

Sternbach left a rich legacy as a scientist whose work contributed to significant advances in medicine and therapeutics. Despite his death in 2005, his contributions to the fields of chemistry and pharmacology are still present and valued.