The Adirondack Chair was originally designed by Thomas Lee around the turn of the 20th century. Lee was vacationing in the Adirondacks (Westport, NY) on the shores of Lake Champlain, and needed some outdoor seating while entertaining family and friends. He designed a few different prototypes and tested them on his family, getting feedback and making adjustments.
That winter, Lee enlisted his hunting friend Harry Bunnell to help him manufacture the chairs. Bunnell was a carpenter and could turn out chairs in his shop over the winter to make some extra money. The chairs were an immediate hit in Westport, and Bunnell filed for a patent (No. 794,777) in the winter of 1904, unbeknownst to Lee. Bunnell continued to manufacture and sell the new "Westport Plank Chair" for over 20 years.
Lee's chair featured straight backs and seats, a design that was updated to to a rounded back and contoured seat in the 1930's by Irving Wolpin.
Many craftsman, artists and weekend woodworkers have tweaked the original design, much like Wolpin. Personal touches were added, and the chair design has been modified countless times over the years.
Today, the term "Adirondack Chair" can be used to describe a wide range of chairs, that usually have a slanted back and arms wide enough to hold a plate and/or drink at mealtime.