From Wikipedia
One account holds that Reuben Kulakofsky (his first name sometimes spelled Reubin; his last name sometimes shortened to Kay), a Jewish Lithuanian-born grocer residing in Omaha, Nebraska, was the inventor, perhaps as part of a group effort by members of Kulakofsky's weekly poker game held in the Blackstone Hotel from around 1920 through 1935. The participants, who nicknamed themselves "the committee", included the hotel's owner, Charles Schimmel. The sandwich first gained local fame when Schimmel put it on the Blackstone's lunch menu, and its fame spread when a former employee of the hotel won a national contest with the recipe. In Omaha, March 14 was proclaimed as Reuben Sandwich Day.
From Me
The Reuben is an awesome sandwich that combines a sharp white cheese like Swiss with the tanginess of saurkraut and grills them on a bitter bread like rye and piles on the corned beef. Top that with a sweet Thousand Island dressing and you have a great sandwich that is an entire meal. But it wouldn't be complete without a big dill pickle and a side of crunchy potato chips.