George Washington proclaimed a National Day of Thanksgiving in 1789, although some were opposed to it. There was discord among the colonies, many feeling the hardships of a few pilgrims did not warrant a national holiday. And later, President Thomas Jefferson opposed the idea of having a day of thanksgiving.
It was Sarah Josepha Hale, a magazine editor, whose efforts eventually led to what we recognize as Thanksgiving. Hale wrote many editorials championing her cause in her Boston Ladies' Magazine, and later, in Godey's Lady's Book. Finally, after a 40-year campaign of writing editorials and letters to governors and presidents, Hale's obsession became a reality when, in 1863, President Lincoln proclaimed the last Thursday in November as a national day of Thanksgiving.
Thanksgiving was proclaimed by every president after Lincoln. The date was changed a couple of times, most recently by Franklin Roosevelt, who set it up one week to the next-to-last Thursday in order to create a longer Christmas shopping season. Public uproar against this decision caused the president to move Thanksgiving back to its original date two years later. And in 1941, Thanksgiving was finally sanctioned by Congress as a legal holiday, as the fourth Thursday in November.