There isn't really a set story as to how brownies came to be but one thing that is generally thought is that they are of U.S. origin. It is believed that they received their name because of their color and because of the mythical pixie-like characters from children's books at the time.
The first brownie recipe dates back to 1896 in the Boston Cooking School Cookbook for little molasses (or brown) cakes baked in separate pans. In 1905, the Boston Globe is said to have printed the first recipe brownie recipe. It is commonly believed that brownies happened by accident; that someone forgot to mix the baking soda when they were making a cake.
Brownies did not gain popularity until the 1920s, when chocolate became more accessible to people in the U.S. Now, brownies are on everyone's "love" list because of their taste.