Rearranging the letters of 'Mark Twain' (author) gives:
Am rank wit.
(by Mike Mesterton-Gibbons by hand) (2005)
Other related anagrams without their own page:
"Samuel Langhorne Clemens (alias Mark Twain)" -> "Men, crank man manages well hilarious tales!" (by Aronas Pinchas by hand) (2009) (pending approval)
"Samuel Langhorne Clemens" -> "Me on manners: all such glee!" (by Mike Mesterton-Gibbons by hand) (2004)
"Samuel Langhorne Clemens" -> "Go! Uncle Sam's meaner 'n Hell." (by Joanne Maria Dagonese by hand) (2002)
"Mark Twain's 'The Adventures of Huckleberry Finn'." -> "Freedom raft-run taken by Huck with sinner slave." (by Tony Crafter using Anagram Genius) (2009) (pending approval)