Julius Schäffer (3 June 1882 – 21 October 1944) was a German mycologist. His contributions include studies on the Agaricales (gilled mushrooms), especially the genus Russula, about which he wrote a monograph in 1933.  Later, he revised the genus in the series Die Pilze Mitteleuropas (1926–1967); his notes were published posthumously by his wife Liesel in 1952 with the help of other mycologists. The work was considered the "authoritative treatment of the group for Central Europe".  One of the Russula species that was first described in this publication was R. laeta.  Schäffer developed a chemical test to help with the identification of Agaricus species. A positive reaction of Schaeffer's test, which uses the reaction of aniline and nitric acid on the surface of the mushroom, is indicated by an orange to red color; it is characteristic of species in the section Flavescentes. The compounds responsible for the reaction were named schaefferal A and B to honor Schäffer. 
Schäffer is the only mycologist of modern times known to have died from consuming poisonous mushrooms, in this case, Paxillus involutus. About an hour after he and his wife ate a meal prepared with the mushrooms, Schäffer developed vomiting, diarrhea, and fever. His condition worsened to the point where he was admitted to hospital the following day, and subsequently developed renal failure, perishing after 17 days.  
Several species have been named in honor of Schaeffer:
- Agaricus schaefferianus Hlavácek 1987
- now Agaricus urinascens (Jul. Schäff. & F.H. Møller) Singer 1951)
- Cortinarius schaefferanus ( M.M. Moser) M.M. Moser 1967
- Cortinarius schaefferi Bres. 1930
- Dermocybe schaefferi (Bres.) M.M. Moser 1986
- Lentinus schaefferi (Weinm.) Rauschert 1988
- now Neolentinus schaefferi (Weinm.) Redhead & Ginns 1985
- Phyllosticta schaefferiae Gonz. Frag. & Cif. 1926
- Russula nauseosa var. schaefferi Kill. 1939
- Russula schaefferi Kärcher 1996
- Russula schaefferiana Niolle 1943
- Russula schaefferina Rawla & Sarwal 1983
- Schäffer, J. (1947). "Beobachtungen an Oberbayerischen Blätterpilzen". Berichte der bayerischen botanischen Gesellschaft 27: 201–225.
- "Aims, Organisation". Deutsche Gesellschaft fur Mykologie e. V. (German Mycological Federation). Archived from the original on 2009-07-15. Retrieved 2011-07-25.
- Anon. (1971). "Review: Schaeffer's Russula-Monographie". Taxon. 20 (1): 173. doi: 10.2307/1218561. JSTOR 1218561.
- "Russula laeta". Catalogue of Life. 2011. Retrieved May 21, 2014.
- Kileci-Ksoll R, Winklhoer C, Steglich W. (2010). "Synthesis of schaefferals A and B, unusual phenylhydrazine derivatives from mushrooms of the genus Agaricus". Synthesis. 2010 (13): 2287–91. doi: 10.1055/s-0029-1218790.CS1 maint: uses authors parameter ( link)
- Lamaison, Jean-Louis; Polese, Jean-Marie (2005). The Great Encyclopedia of Mushrooms. Cologne, Germany: Könemann. p. 35. ISBN 978-3-8331-1239-3.
- Beuchat, Larry R. (1987). Food and Beverage Mycology. New York, New York: Springer. p. 394. ISBN 978-0-442-21084-7.