August Paul von Wassermann (21 February 1866 – 16 March 1925) was a German bacteriologist and hygienist.
Born in Bamberg, with Jewish origins, he studied at several universities throughout Germany, receiving his medical doctorate in 1888 from the University of Strassburg.  On September 1, 1891, he entered the newly established Institute for Infectious Diseases, headed by Koch, as an unpaid assistant in both the scientific and clinical divisions, working under Bernhard Proskauer. In February 1893 he became a temporary assistant assigned to problems related to cholera, and from February 1895 to June 1896 he was inspecting physician at the Institute’s antitoxin control station for diphteria, which was transferred in 1896 to the Institute for Serum Research and Testing in the Berlin suburb of Steglitz. Wassermann then returned to the institute itself as an unpaid assistant.
Some felt that Wassermann carried on his investigations as a hobby, and he certainly did not need to earn a living. He was small in stature but, contrary to assertion, he was not stooped or hunch-backed, and he had bright blue (not dark) eyes. He always dressed with extreme elegance.
He was an impulsive man and a superb speaker, expressing his conclusions openly without scientific inhibitions. It was said that his theoretical knowledge was rather weak and that his practical application was not at all that good either, but that he relied on a number of technicians to do his biddings in the laboratory. These were dubbed his scientific coolies. He had an outstanding capacity to render complicated theoretical problems comprehensible to the uninitiated. 
In 1906 he became director of the division for experimental therapy and serum research at the institute, followed by a directorship of the department of experimental therapy at the Kaiser-Wilhelm-Gesellschaft for the Advancement of Science in Berlin-Dahlem (1913).
Wassermann developed a complement fixation test for the diagnosis of syphilis in 1906, just one year after the causative organism, Spirochaeta pallida, had been identified by Fritz Schaudinn and Erich Hoffmann. The so-called "Wassermann test" allowed for early detection of the disease (despite its nonspecific symptoms), and thus prevention of transmission. He attributed the development of the test to earlier findings of Jules Bordet and Octave Gengou (complement fixation reaction) and to a hypothesis introduced by Paul Ehrlich in his interpretation of antibody formation.
The Wassermann test remains a staple of syphilis detection and prevention in some areas, although it has often been replaced by more modern alternatives. With Wilhelm Kolle, he published the six-volume Handbuch der Pathogenen Mikroorganismen (Handbook of Pathogenic Microorganisms). 
With Rudolf Kraus (1868-1932), Wassermann was co-founder of the Free Association for Microbiology, and he served as president of the Academy for knowledge of Judaism. Although occasionally sarcastic, he was always helpful and kind, even under different conditions. He once characterized himself as a "laboratory worker.” His many honours included orders and decorations from Prussia, Belgium, Japan, Romania, Spain, and Turkey.
In 1921 Wassermann was the first recipient of the Aronson Foundation Prize. However, he was never appointed to a chair at the prestigious Berlin faculty, and was never awarded the Nobel Prize, to which he is said to have been a candidate. In 1895 he married Alice von Taussig of Vienna; they had two sons.