While agar itself has been used in Japan for centuries, its introduction and popularization in microbiology is credited to Frau Fanny Hesse, the wife of German bacteriologist Walther Hesse.

Here's a breakdown:

* Agar itself: Agar was originally used in Japan as a food thickener and gelling agent, derived from seaweed.

* Fanny Hesse's contribution: In 1881, while working with her husband in his lab, she suggested using agar to solidify the nutrient broth used for growing bacteria. This was a crucial breakthrough as previous methods with gelatin had limitations like being melted at room temperature and susceptible to bacterial digestion. Agar, being heat-resistant and less susceptible to bacterial degradation, proved to be a much better option.

* Walther Hesse's work: Walther Hesse then used agar to cultivate bacteria, paving the way for significant advancements in microbiology.

Therefore, although the discovery of agar was not by the Hesse's, their adaptation and implementation of it for cultivating bacteria in the lab earned them recognition as the "inventors" of agar in microbiology.