In political letters throughout history, the closing "Your Obedient Servant" appears many times (For example, president Lincoln uses it in all of his letters). Where and how did this phrase originate and how did its usage develop?
Early specimens of 'your obedient servant'
The earliest Google Books match for "your obedient servant" at the close of a letter is from a letter from an Englishman (from York) contained in George Smith, The Compleat English Grammar (1758), as part of a somewhat more elaborate leave-taking:
Sir your friend
your obedient Servant
and Unfeigned friend.
The same Google Books search finds a match from The Gentleman's Magazine, or Monthly Intelligencer (June 1742), involving an interview with "Landois the Second," a courtier, originally published in Common Sense. In this instance, the phrase comes at the close of the interview:
A, Sir, I thank you. We are the Chancellor of the Exchequer's most humble Servant,———by his good conduct we have gain'd Part of your Trade, and humbled our Enemies upon the Continent———long, very long may he rule over you for our Sakes; but if he was our Chancellor of the Exchequer, we should serve him a Trick that I do not much care to tell;———however, I am obliged to you for your Information, and am your obedient Servant, &c.
And a translation (from Spanish) of the closing to a brief letter from General Wall to the Spanish ambassador on reprinted in Papers Relative to the Rupture with Spain (1762) ends with this:
Most Excellent Lord, I kiss your Excellency's Hands,
Your obedient Servant,
Don RICARDO WALL
But the Google Books search's earliest formal and succinct "your humble servant" in English-language letter closures are from the 1770s. The first appears in a letter from Walter Shirley to John Fletcher, reprinted in John Fletcher, A Vindication of the Rev. Mr. Wesley's Last Minutes (1771):
I am SIR, Your obedient Servant, WALTER SHIRLEY.
Then from William Tryon to Jonathan Trumbull written on April 17, 1778, and reproduced in The Town and Country (July 1778):
I am, Sir, your obedient servant, W. TRYON.
(In his letter of response to Tryon, Governor Turnbull used the equally polite wording "I am, Sir, your humble servant," leaving us to decide whether a humble servant or an obedient one is the more conformable to one's will.)
And the other in a letter from George Johnstone to Robert Morris, written on June 16, 1778, and reproduced in The Edinburgh Magazine, and Literary Miscellany (October 1778):
I am, with affection and esteem, dear Sir, your obedient servant, Geo. Johnstone.
The Shirley letter was written and published in England, but both of the 1778 instances involve American correspondents—and indeed there appears to have been a vogue of this usage in the United States in the late 1700s.
The wording "Your obedient servant" was fairly common in both the United States and Great Britain by 1800.
Early specimens of 'obliged and obedient' (and often humble) servants
The lengthier sign-offs of the "obliged and obedient" school are spread across the late 1600s and much of the 1700s. I will try to provide a representative selection of these florid farewells, both with regard to year of writing and mode of expression. First, from William Temple to the King, written on December 4, 1674, published in Letters to the King, the Prince of Orange, the Chief Ministers of State, and Other Persons, volume 3 (1703):
The Knowledge of all worth your Majesty's Trouble from hence, will, I know, be transmitted from my Lord Chamberlain, and leave me no other Part than that of my Humble Acknowledgments upon the Confidence your Majesty has been pleased to express of me in so great Occasions, and the plain Offers of that very Sincere Devotion, wherewith I am, and shall ever be,
Your Majesty's most Loyal
Subject, and most Obedient
From a letter from F.E. to "your grace" written some time in 1688 and reprinted in The State Letters of Henry, Earl of Clarendon, Lord Lieutenant of Ireland During the Reign of K. James the Second (1763):
God send your grace a good night, and a happy morning. I am
your obliged and obedient servant,
From a supposed letter from Lady Lizard to the author, in Addison & Steele's The Guardian (April 30, 1713):
Your most Obliged,
and Obedient Humble Servant,
From a letter from Richard Steele to the clergy of the Church of England, in The Political State of Great Britain (January 1714):
And as there are no Instruments under Heaven so capable of this great Work, that God would make you such to this divided Nation, is the hearty Prayer of, GENTLEMEN, Your most dutiful, and most obedient Humble Servant, RICHARD STEELE.
From the epistle dedicatory to the second edition of William Petty, The Political Anatomy of Ireland, 1672 (1719):
May it please your Lordship,
Most obliged, and most
Obedient, Humble Servant
From a letter from A, Ramsay to Jonathan Swift, written on August 1, 1727, in Letters Written By The Late Jonathan Swift, D. D. Dean of St. Patrick's, Dublin; and Several of His Friends, volume 2 (1768):
I am with the utmost regard and esteem, reverend Sir, your most humble, and most obliged, obedient servant,
From a letter from B. Motte to Jonathan Swift, written on October 4, 1735, and reprinted in Letters Written By The Late Jonathan Swift, D. D. Dean of St. Patrick's, Dublin; and Several of His Friends, volume 4 (1766):
I have been so particular (I fear even to tediousness) in that letter, that I have nothing to add, but a repetition of the sincere profession I there made, that I am, with all possible gratitude, truth, and sincerity, Sir, your obliged and obedient humble servant,
From an epistle dedicatory to the commissioners of the Royal Hospital at Chelsea in John Woodman, The Rat-catcher at Chelsea College: A Tale (1740):
...that every one on this Board may so encourage and promote a Design, propos'd entirely for Good and Use of the Publick, that he may say with more Justice than Horace did, "Exegi Monumentum ære perennius," is the ardent Prayer and Expectation of,
Most obedient humble Servant,
From a letter written by John Spencer to the citizens of Bristol, England, reprinted in The Whitehall Evening Post Or London Intelligencer (1756):
...and assure you, I shall always continue to wish the utmost Prosperity to the City of Bristol, and am,
Your obliged and obedient humble Servant,
Then, from a letter from Richard Grindall to William Watson, written on December 7, 1857, and reprinted in The Universal Magazine (1758):
I am, with respect,
Your obliged and obedient Servant,
In a letter from John Morgan to the Sheriff of Herfordshire, written on June 10, 1763, and published in The London Magazine; Or, Gentleman's Monthly Intelligencer (1763):
I am, Mr. Sheriff,
Your obliged and obedient
And in a letter from George Washington to John Jay, written April 14, 1779, and reprinted in The Life of John Jay: With Selections from His Correspondence and Miscellaneous Papers, volume 2 (1833):
With the truest esteem and personal regard,
I am, dear sir,
Your obliged and obedient servant,
Today, "Your obedient servant" may sound extravagant and highly ornamental; but in the second half of the eighteenth century, when it first became popular, it must have sounded almost brusque, arriving as it did after many decades of truly elaborate declarations of loyal and grateful servitude.
The short answer to the question "Where did 'Your obedient servant' originate?" is "In abject expressions of admiration of and devotion to powerful people by letter writers, book writers, and other supplicants seeking patronage, ingratiation, and in some cases forgiveness." The form later carried over to exchanges between equals, just because it seemed respectful and polite, and at some point received a pairing down to "Your humble servant"—and from there, perhaps, to the even more abrupt "Yours truly," "Sincerely yours," or just "Yours."