Dmitri Ivanovsky

Dmitri Ivanovsky was a Russian botanist who, investigating tobacco mosaic disease in 1892, found that sap from infected plants remained fully infectious after being passed through a Chamberland filter fine enough to remove every known bacterium. He interpreted the result as a bacterial toxin rather than a new kind of infectious agent, so the discovery's full significance was not recognized in his lifetime. Martinus Beijerinck reached the same experimental result independently six years later and correctly identified the agent as a new class of pathogen, which he named a virus. Ivanovsky and Beijerinck are jointly credited as the discoverers of viruses, though both died before the finding was honored with a Nobel Prize.