Aloha, Kim. Odd coincidence--I have just completed  1866 in my comprehensive
chronology, "Mark Twain, Day-by-Day," and have read all  25 letters of Sam's
to the Sacramento Union. Yes, I believe it was Sanborn who  compared the use
of an alter-ego, in this case "Brown," to Sancho Panza.

The source of the name "Brown" is, I  believe, William Brown, the
Mississippi
Steamboat pilot: E2809Ca middle-aged, long, slim, bony, smooth-shaven,
horse-faced, ignorant, stingy, malicious, snarling, fault-hunting,
mote-magnifying
tyrant," Who Sam had to "pound some" in that tiff on June 3,  1858.

The  alter ego literary ploy was used by Sam with his rival in Virginia
City,
 Clement, whom he called "Unreliable." Sam loved a spoof, and also loved to
exaggerate. Carrying a grudge wasn't beyond him either. Sam used people he'd
known or met in so many of his stories.  William Brown the nasty riverboat
pilot was only one, but one who was vivid in Sam's memory.

The  Brown of the Union letters allowed Sam to make fun of customs, natives,
habits and the like without taking the heat for it. Such poking fun of
foreigners gave the home audience a secure and high-minded reassurance. The

contrast with Brown allowed Sam, the reporter/narrator, to be seen in a more

favorable and acceptable light. So, yes, I agree with Sanborn that Sam's use
of Brown, is indeed an alter-ego sidekick.  In the Sagebrush  Bohemian,
Nigey Lennon
wrote, "Just as he had used Clement Rice as 'The  Unreliable' to good
advantage, Twain created 'Mr. Brown,' ostensibly his  traveling companion
during the
Sandwich Islands jaunt, but in reality a catchall  for every crude impulse
Twain himself experienced and was ashamed to call his  own." p123. I'm not
so
certain that Twain was ashamed of much--but this gave him  a way to express
some of his crude humor without pissing off the editors and  readers of the
Sacramento Union, from whom Sam depended on a living  over the next five
months.

In  my research I discovered that Sam wrote many of the letters days after
the fact,  or when he'd returned to Honolulu. He even dated one "September
10th"
when he left the Islands aboard the sailing ship Smyrniote  July 19th 1866.


Hope this helps,

David H. Fears
Mark  Twain, Day by Day - a comprehensive, daily chronology in  progress