Mark Twain is nom de plume (a name used by an author instead of his rea name). It has no middle part. The author who used the name Mark Twain was Samuel Langhorne Clemens.
Shania Twain
Susy Clemens, Mark Twains favored daughter.
Samuel Langhorne Clemens
Writing
The real name of the American author Mark Twain was Samuel Langhorne Clemens (1835 - 1910).
Mark Twain was the 'pen-name' of Samuel Langhorne Clemens
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Mark twain liked visiting libraries as a youngster.
Mark Twain's first name was Samuel. His full name was Samuel Longhorne Clemens.
Mark Twain's first job was as a typesetter.
November 30th 1835
It was Susy Clemens.