Noah Webster (Wiki commons - Appletons' Cyclopædia of American Biography)
Noah Webster’s first dictionary, A Compendious Dictionary of the English Language, appeared in 1806 serving as the launch vehicle for his magnum opus the American Dictionary of the English Language. This he completed in Cambridge, England of all places in 1825 and it hit the streets in 1828. Webster was some act to follow, it is claimed that he learned twenty-six languages, including Old English (Anglo-Saxon), Greek, Hebrew and Latin in order to evaluate the etymology of words. Incredibly, his dictionary seems to have been a single-handed production defining over 70,000 words. So you see Doctor Johnson this determines the proportion of an American to an Englishman as opposed to determinations of the proportion of an Englishman to a Frenchman.
This dictionary can be regarded as a fork in the development of UK and American English since Webster is credited with introducing, or at least formalising, the odd (or simplified) way in which Americans spell such things as: marvelous licorice, colored plow, and fetid odor. Webster himself died soon after publication of the second edition which added a further 5,000 words to his dictionary and later editions were published under the Merriam-Webster brand. This brief description is included because, as you will see, the Webster was used as both benchmark and beater during the slow evolution of the OED.