The name is French, first documented in 1835, based on the Latin "birretum" (which also gives us birreta, a square cap traditionally worn by Roman Catholic bishops).
Despite its association with the artistic elite in modern times, at the point in the 17th Century when Dutch masters Rembrandt and Johannes Vermeer painted their self-portraits, a beret was a peasant hat not yet called a beret, with a long history dating back to at least the Bronze Age. Landscape painters in particular favored it for its practicality in all manner of weather; for similar reasons (ease of manufacture, the ability to be dyed in various colors), the beret became associated with various militaries and revolutionary political movements, a trope in its own right which later rose to even further prominence among the Allies in World War II, and continues into the present day.
The black beret as a fashion among Parisian women (and mimes) first appeared in the early 1900s, and while the history is always vague, it seems as if it was a combination of all of the above — solidarity with the common people, the world at war, Paris chic and Beatnik flair — that led to the beret becoming part of the the uniform for artists of the day.
Osamu Tezuka, the so-called Father of Manga, was almost never seen without his beret. As such, many uses of the beret in anime and manga are a Shout-Out to him.
