Smith, Theobald (1859–1934), a United States pathologist. His investigations of infectious diseases led to the discovery, with F. L. Kilborne, that the parasite causing Texas cattle fever is carried by a cattle tick. Smith discovered the difference between human and bovine tuberculosis and contributed to the development of vaccines for human and animal diseases.

Smith was born in Albany, New York. After graduating from Albany Medical College in 1883, he directed the newly created pathological laboratory of the Bureau of Animal Industry in the U.S. Department of Agriculture. He taught at Harvard University (1895–1915), then joined the Rockefeller Institute for Medical Research.