Paul Walden (1863 – 1957) was a Latvian chemist with German background. He was born in the castle Rosenbeck in Wenden near Cēsis in Latvia and initially studied at the University of Riga and St. Petersburg before receiving his doctorate at the University of Leipzig in 1891 with Wilhelm Ostwald.
Walden left Latvia after the Russian Revolution and accepted positions in Germany. The Walden inversion is named after him. Walden also invented ethylammonium nitrate  as the first example of an ionic liquid. Walden is also known for his 1949 book, History of Chemistry, an excellent synthesis of contemporary historical research in the field.