Dewar's 12yr blended scotch is "double aged" taking 12yr scotch whiskies and then returning them to oak for a final "marrying" of flavors.
As the name might suggest, the company John Dewar and Sons was founded in 1846 by founder John Dewar, Sr and his sons John, Jr and Thomas Dewar. The began in 1846 as a seller of spirits and began experimenting with what turned out to be very popular blends. They were the first company to offer its scotch in bottles rather than simply casks. They went through a series of ownership changes--as many companies in Scotland did--in the latter half of the 20th century. They were finally sold to Bacardi in 1998. Today they own a number of different, well-known distilleries (themselves under the umbrella of Bacardi) that contribute to their blends as well as producing their own single-malts.