Johann August Ernesti was a man who lived a long, long time ago. He was born in the year 1707 and he died in the year 1781. He was a German scholar who studied and wrote a lot about things like grammar, language, and literature.
You know how we have rules for how we speak and write in English, like when we use capital letters, when we put commas, and when we end a sentence with a period? Well, Johann August Ernesti helped create some of those rules in the German language.
He also wrote books and taught people about Latin, which is a very old language that people used a long time ago. He was very good at understanding how languages work and how to make them better.
Even though Johann August Ernesti lived a long time ago, his work helped many people learn and understand language and literature better.