Which author wrote a series of humorous letters under the pen name Thomas Jefferson Snodgrass?

Samuel Langhorne Clemens (November 30, 1835 – April 21, 1910), better known by his pen name Mark Twain used many different pen names in his early career (another was W. Epaminandos Adrastus Blab) and in the 1850s he used for a short time, Thomas Jefferson Snodgrass.

This particular pen name is of note because this is one of the first times that Clemens begins to write in the vernacular. Snodgrass becomes something of a character for Clemens; as Kent Rasmussen puts it, "he makes 'Snodgrass' a country bumpkin with atrocious spelling and grammar...who comments disdainfully on big city life."In three letters that Clemens gets published in the Keokuk post, Snodgrass describes a trip on the railroad, seeing a play, and "a adventure".