Who discovered Bacteriophage?

De Herelle discovered Bacteriophage.
A bacteriophage, also known informally as a phage, is a duplodnaviria virus that infects and replicates within bacteria and archaea.
De Herelle called the virus a bacteriophage, a bacteria-eater. He also recorded a dramatic account of a man suffering from dysentery who was restored to good health by the bacteriophages.
It was de Herelle who conducted much research into bacteriophages and introduced the concept of phage therapy.