The booklet 'Mourt's Relation' (full title: A Relation or Journal of the Beginning and Proceedings of the English Plantation Settled at Plimoth in New England) was written primarily by Edward Winslow, although William Bradford appears to have written most of the first section. Written between November 1620 and November 1621, it describes in detail what happened from the landing of the Mayflower Pilgrims inside Cape Cod (became Provincetown Harbor), through their exploring and eventual settling of Plymouth Colony; the book describes their relations with the surrounding native Americans, up to what is commonly called the first Thanksgiving and the arrival of the ship Fortune in November 1621. Mourt's Relation was first published in London in 1622, presumably by George Morton, sometimes called George Mourt (hence the title "Mourt's Relation").
An English Puritan Separatist who had moved to Leiden, Holland, Morton stayed behind when the first settlers left for Plymouth, Massachusetts, but he continued to orchestrate business affairs in Europe and London for their cause—presumably arranging for the publication of and perhaps helping write Mourt's Relation. In 1623 Morton himself emigrated to the Plymouth Colony with his wife Juliana, the sister of Governor William Bradford's wife Alice. But George Morton didn't survive long in the New World: he died the following year, in 1624.
George Morton's son Nathaniel Morton became the clerk of Plymouth Colony, a close adviser to his uncle Governor William Bradford, who raised him after the death of his father, and the author of an influential early history of the Plymouth Colony, "New England's Memorial." A four-decade long tradition at The Wall Street Journal, is to reprint the section on the "first Thanksgiving," on the Wednesday before the holiday.
While the booklet was summarized by other publications without the now familiar thanksgiving story, by the eighteenth century the original booklet appeared to be lost or forgotten. A copy was rediscovered in Philadelphia in 1820, with the first full reprinting in 1841. In a footnote the editor, Alexander Young, was the first person to identify the 1621 feast as "the first Thanksgiving."