Friedrich Löffler was a German bacteriologist, best known for his discovery (in association with Edwin Klebs) of the organism that causes diphtheria, Corynebacterium diphtheriae (Klebs-Loffler bacillus). He also made several discoveries in veterinary medicine, such as the cause of swine fever and plague, the causative organism of glanders, and the fact that foot-and-mouth disease is caused by a virus.