As far as I've been able to tell through clever googling in my favorite search engine, the renowned and much beloved Pirate Resignation Letter was written by Chris Castle and delivered to James Bear (deceased), former managing partner of Knobbe, Martens, Olson & Bear, LLP.
After using the letter, Castle shared it with his friend, user "Otter Von Pop" of the (now defunct) BirdSunEye.com forum, and that user posted it on 17 October 2003 both as a forum post and as a Word doc attachment.
Later that morning, Chris Castle, posting as "The Bartender" confirmed the story and reported on the (first ever!) recipient's humorless (or brilliantly funny!) reply.
Harvested from the past and hosted right here on Popehat is that original forum thread:
Enjoy this bit of net.history! And if you have anything to add about the people or circumstances, please share what you know in the comments.
UPDATE: There's a new pretender to the helm!