Paul Walden was Latvian-German scientist. His work in stereochemistry and the history of chemistry lead to multiple breakthroughs in the field of chemistry. Perhaps most notably, his name is remembered through the “Walden inversion”, a stereochemical reaction that he invented. He is also well-known for having synthesized an ionic liquid at room temperature, achieving the feat with ethylammonium nitrate. Walden worked as chemistry professor at various European universities, where he was highly lauded for his skills as a lecturer as well as for his breakthroughs in the laboratory. Living and working in early-20th century Europe, some of Walden’s activities were interrupted during the two World Wars. While he was nominated for a Nobel Prize in 1913 and 1914, the First World War interrupted that period of his work as well as the recognitions. Nonetheless, he lived a long life, lecturing and working until his final years. Today, his work is regularly commemorated by the scientific community and particularly in Latvia, where he was born and spent many of his busiest years. Given the importance of the Walden Inversion, he is often referred to as the founder of physical organic chemistry.