David Gruby (August 20, 1810 – November 14, 1898) was a Hungarian physician who was born in the village of Kis-Kér (now Bačko Dobro Polje, Serbia). He received his doctorate in Vienna and performed scientific research in Paris.
Gruby is remembered as a pioneer in the fields of microbiology and medical mycology. Most of his important work was done during the 1840s. In 1841 he described the fungus that causes favus. This discovery was independent of Johann Lukas Schönlein's (1793–1864) findings. Today, this fungal parasite is called Achorion schoenleinii in Schönlein's honor.
In 1842 he described a microscopic cryptogam (trichophyton ectothrix) which causes a dermatological disease known as sycosis barbae. Gruby also discovered Monilia albicans, the cause of candidiasis, and in 1843 he described a fungus (Microsporum audouini) that causes a type of ringworm. This fungus was named after naturalist Jean Victor Audouin (1797–1842), and the disease is sometimes referred to as "Gruby's disease".
Gruby also discovered a parasite in the blood of frogs he called Trypanosoma sanguinis. During the early years of anaesthesia, he performed important experiments with chloroform and ether on animals.