The story of the Penny Black, the world's first-ever adhesive postage stamp, begins with a man named Rowland Hill who triggered a period of vast postal reform.
Hill, an English teacher, inventor and social reformer, calculated that it made more financial sense to price deliveries by weight.
Until then, the cost of delivery of a letter was paid by the recipient - and the price was dependent on the number of miles travelled and the size of the letter.
To support his new theories, Hill drafted a pamphlet entitled Post Office Reform: its Importance and Practicability.
The pamphlet was circulated in 1837 and, marked "Private and Confidential", was passed to Thomas Spring-Rice, the Chancellor of the Exchequer.
But Hill's plan for progress was not without its obstacles. In the House of Lords, the Postmaster Lord Lichfield angrily dismissed the pamphlet's "wild and visionary schemes."
William Leader Maberly, Secretary to the Post Office, echoed Lichfield's sentiments: "This plan appears to be a preposterous one, utterly unsupported by facts and resting entirely on assumption."
Nevertheless, merchants, traders and bankers viewed the existing postal system and corrupt and restraining to their respective trades.
The groups formed a so-called "Mercantile Committee", and pushed for Hill's plans to be given a chance. In this case, their 'people power' worked.
Hill was given a two-year contract to run the new system, which led to the passage of the Penny Postage Bill in 1839.
As a result of Hill's actions, Great Britain subsequently became the first county to produce an adhesive postage stamp.
That stamp, the 1d. Penny Black, entered circulation on May 6, 1840. It remained in use for little over a year, during which time 286,700 sheets and 68,808,000 stamps were printed.
The introduction of the Penny Black was a revolution in communication. It was the Victorian equivalent of the internet, and an invention which changed the world.
The stamp was an instant success with the public. Within seven months, over 160 million letters had been sent - doubling the number of letters sent in the previous year.
Letters were now being sent to all corners of the globe with increased frequency and, by the turn of the century, more than 2.3 billion letters had been posted.
The rest is history, and the Penny Black spearheaded a way of posting letters which is still relied upon today.
What's more, it is because of the Penny Black that we today have the hobby of philately.
The world's first-ever adhesive postage stamp - and also one the most collectible
Today, a Penny Black can be purchased for as little as £10. However, this will only get you a used and poor-quality example.
However, the value is in finding mint (unused) examples, of which few exist. And pairs and blocks of four are worth significantly more.
The original gum on a Penny Black is often said to be the most valuable substance on earth by weight. Without it, a mint Penny Black can lose up to 90% of its value.
But if the gum is untouched and as fresh as the day it was printed, this can add a significant premium to the price.
Until recently, the world record for a single mint Penny Black was $156,000 at a Danish auction house, in 2004.
That was surpassed by British stamp dealers Stanley Gibbons, who sold a single marginal example for an incredible £250,000 in 2009.
Penny Black First Day Covers, issued on 6th May 1840, are also highly sought after. Today, approximately 78 are known to exist.
The most famous of all is the Kirkudbright cover that was purchased by The Royal Philatelic Collection of Her Majesty Queen Elizabeth II in 2004.
The cover is believed to have sold for £250,000 at the time. It is now estimated to be worth £500,000.