Brewers call malt "the soul of beer" but they might also add that malt contributes mightily to the different personalities we expect from beer. Of all the barley grown, only one-quarter or less is used for malting.
Malt was an important product long before the days of recorded history. Across many centuries the process of production has changed greatly, but malt as a finished product is much the same, changing probably only to the extent that better grades of barley have been developed.
Malt is the product created through controlled germination and drying (or kilning) of barley, and consists of three stages. Click on the image below to see the full size chart, or read a description of the how and why.