Today in the history of the American comic strip: June 12

American cartoonists and writers may not have invented the comic strip, but some argue that the comics, as we know them today, are an American creation. Clearly, the United States has played an outsize role in the development of this underappreciated art form.

6.12.1938: Prince Valiant's title character receives the Singing Sword, a charmed blade, from Prince Arn of Ord. Hal Foster created the strip in 1937. 

Most of the information listed here from one day to the next comes from two online sites -- Wikipedia, and Don Markstein's Toonopedia -- as well as 100 Years of American Newspaper Comics, edited by Maurice Horn. Note that my focus is on American newspaper comic strips (and the occasional foreign strip that gained popularity in the United States). Thus, comic books and exclusively online comics are not included here.