Leopold Ružička ForMemRS (Croatian pronunciation: [rǔʒitʃka];[3] born Lavoslav Stjepan Ružička; 13 September 1887 – 26 September 1976)[5] was a Croatian-Swiss scientist and joint winner of the 1939 Nobel Prize in Chemistry "for his work on polymethylenes and higher terpenes"[6][7] "including the first chemical synthesis of male sex hormones.

"[8] He worked most of his life in Switzerland, and received eight doctorates honoris causa in science, medicine, and law; seven prizes and medals; and twenty-four honorary memberships in chemical, biochemical, and other scientific societies.

His family of craftsmen and farmers was mostly of Croat origin,[9] with a Czech great-grandparent, Ružička, and a great-grandmother and a great-grandfather from Austria.

[5] Owing to the excessive hardship of everyday and political life, he left and chose the High Technical School in Karlsruhe in Germany.

That is why his physical chemistry professor, Fritz Haber (Nobel laureate in 1918), opposed his summa cum laude degree.

He investigated the ingredients of the Dalmatian insect powder Pyrethrum (from the herb Tanacetum cinerariifolium), a highly esteemed insecticide found in pyrethrins, which were the focus of his work with Staudinger.

Ružička later said of this time: "Toward the end of five and a half years of mainly synthetic work on the pyrethrins I had come to the firm conclusion that we were barking up the wrong tree."

[10] With expertise in the terpene field, he became senior lecturer in 1918, and in 1923, honorary professor at the ETH (Eidgenössische Technische Hochschule) as well as the University of Zurich.

Here, with a group of his doctoral students, he proved the structure of the compounds muscone and civetone, macrocyclic ketone scents derived from the musk deer (Moschus moschiferus) and the civet cat (Viverra civetta).

He also developed a method for synthesising macrocycles, now known as the Ružička large ring synthesis,[17] which he demonstrated by preparing civetone in 1927.

After the successful synthesis in 1935 of sex hormones (androsterone and testosterone),[20] his laboratory became the world centre of organic chemistry.

[6] Over the period 1934–1939 he published 70 papers in the field of medicinally important steroid sex hormones, and filed several dozen patents besides.

[22] During World War II, some of his excellent collaborators were lost, but Ružička restructured his laboratory with new, younger and promising people; among them was young scientist and future Nobel laureate Vladimir Prelog.

He insisted on a better organization of academic education and scientific work in the new Yugoslavia, and established the Swiss-Yugoslav Society.

[5] At ETH Zurich, the Ružička Award was established in 1957 on the occasion of his retirement, for young chemists working in Switzerland.