Released by Rolex in 1945 to celebrate the company's 40th (Jubilee) anniversary, the Datejust is one of the earliest Rolex models that is still around today. It was the first automatic wristwatch that sported an automatic date window, a radical, new feature back in the 40s. Initially, the Datejust was only made available in 18k yellow gold, but over the years the watch saw many variations in design (including stainless steel and two-tone versions in 1957 and 1962 respectively).
The modern Datejust comes in a wide variety of material combinations (yellow/rose/white gold, two-tone, stainless), bracelet styles (Oyster, Jubilee), dial configurations (plain, diamond set), bezels (domed, fluted, diamond set), etc., with reference 116200 Oyster Perpetual being the standard for today's 36mm Datejusts. This is the case diameter for the largest Datejust, but their sizes go all the way down to 26mm for Ladies models.