Porter originates from turn of the 18th Century London. At that time one of the most popular drinks was called 'Three Threads'. This was a blend of three different sorts of ale; pale ale, brown ale and old ale. The problem for the London-based brewers was that old ale had to be matured in huge barrels for a year and there simply wasn't the space for it in the city. So the publicans had to buy it in from the country-based brewers who, having a strangle hold on the market, charged extortionate prices for their beer.
The Birth of Porter
Many London brewers tried to imitate 'Three Threads' but the resulting brew didn't sell very well until, in 1722, a chap named Ralph Harwood made a beer that he called 'Entire Butt'. This went down extremely well with most people because it was similar to 'Three Threads' but was a lot cheaper. The landlords liked it because it only took up one space in the cellar and didn't need mixing like the other three beers and was cheaper. Ralph Harwood liked it because it made him a lot of money. However, country-based brewers didn't like it as pubs stopped buying their over-priced old ale.
Many other brewers imitated the 'Entire Butt' and it fast became the staple drink of the working classes, or as they were known at the time, the 'porters', giving the style of beer its name. The stronger varieties of porter became known as 'stout porters' and when the popularity of porter was in decline 'stout porters' had a loyal following of drinkers who kept those breweries who specialised in 'stout porters' in business. Eventually the porter part was dropped from the name and the 'stout' brand was born.