The porter style of beer originated in London and was originally a mix of a brown ale, and old ale, and a mild ale. The style was named after London's transportation workers who were called Porters and were quite fond of the style.
The two major types of porter beer are the English Porters and the American Porters. Colonial Americans imported their porters from England until they gained their independence and then they began to brew their own versions of this style.
English Porters are usually dark in color, just short of black with many having reddish-brownish hues when held up to light. Their roast character is greater than Brown ales but less than stouts and usually more smooth and chocolatey as compared to the sharp espresso like bite that is so often found in stouts. Porters are usually complex with many different flavors and have ABV’s in the 5% range.
American Porters are also dark in color with roasted flavor that is a little smoother. The beer usually uses roasted grains and flavors of caramel. While the color may scare many people away, American porters are usually very smooth and while the bodies are deep and complex, they are fairly mellow.
A local Albany example of the porter style is Brown's Brewing Company's Whiskey Porter. Brown's Whiskey Porter is one of my all-time favorite Albany beers and was the 2008 World Beer Cup Silver Cup Winner. The beer starts out as an English Porter and is then aged in bourbon whiskey barrels for two months. While the beer checks in at a fairly modest 5.75%, the beer is a monster. The body is extrememly rich and complex with plethera of flavors ranging from hints of whiskey, chocolate, dark malts, and caramel.