The precise ingredients of the world's best-selling Scotch whisky brand are, unsurprisingly, a closely-guarded secret. Johnnie Walker, in all its various guises, may have shifted over 156 million litres around the globe in 2016, but only a handful of people know all the secrets of its winning recipes.
However, what is well-known in the whisky world is that one of the most important ingredients in the Johnnie Walker blends is a light but distinctive Speyside single malt called Cardhu.
And the person whose job it is to ensure that the Cardhu distillery fulfils its commitments to that global brand is Northern Ireland man Andrew Millsopp.
Andrew (40) is Cardhu group senior manager for the drinks giant Diageo, which owns 28 distilleries across Scotland.
Born in Craigavon, Andrew has spent his working life in the brewing and distilling industries. As group senior manager, he's currently responsible for four Diageo distilleries in the Cardhu group.
Andrew spent much of his early life in Newry and went to school there.
His father Kenny is not long retired after a career in the fire service that took him to Belfast, Omagh and headquarters in Lisburn.
Upon leaving school, Andrew had thought of a career in dentistry but eventually decided against it and instead went to university in Edinburgh to undertake a course that focused on biological and chemical sciences.
The latter part of the course included a focus on brewing and distilling and it was this aspect that began to intrigue him more and more.
"I became very interested in the whole process and I saw that most of the guys who followed this route got pretty good jobs afterwards," he says.
"Distilling was very difficult to get into at that time," Andrew recalls.
"A lot of the people on my course ended up in medium-sized breweries in England.
"It was very unusual to progress from my course into distilling. In a lot of places the distilleries only took people from the local area.
"Anyone they employed was usually replacing someone who had worked in the business for a lifetime.
"Unlike today, when there are many opportunities in the industry for young people and some great apprenticeships on offer, there were very few people under the age of 30 in distilling back then."
So, like many of his fellow students at that time, Andrew started out in brewing and one of his earliest jobs was at the Harp brewery in Dundalk.
However, his ambitions still lay in distilling and that persistence finally paid off when he landed a job at the Oban distillery on the west coast of Scotland.
From there, he went on to distilleries the length and breadth of Scotland and also spent some time back in Northern Ireland at the Bushmills distillery.
Job followed job as he built up huge experience in the industry, from Royal Lochnagar on the Balmoral estate to overseeing the Diageo distilleries on the famous whisky island of Islay.
"I worked it out recently that I must have moved house 22 times," he says with a smile.
Now settled on Speyside with his wife Lorna, a teacher, and children Ciara and Christopher, Andrew lives in a village a few miles from where Cardhu (pronounced Car-doo) nestles among the gentle uplands near Inverness.
As well as producing its own single malts (they're "incredibly popular" in France, Spain and Greece, says Andrew), Cardhu is a crucial component of the Johnnie Walker range.
Whisky aficionados will tell you that Johnnie Walker simply wouldn't be Johnnie Walker without Cardhu.
It's no accident that this was the first distillery to be bought by John Walker and Sons as their business rapidly expanded in the late 19th century.
It was purchased in 1893 from the Cumming family shortly after they had purchased new distilling equipment that tripled Cardhu's output, most of which was being swallowed up in the production of Johnnie Walker.
Walker had started his whisky business after selling the family farm in 1819 to start a grocery shop in Kilmarnock.
The forerunner of today's global brand was Walker's Old Highland Blend introduced by John's son Alexander in 1857.
The company adopted a unique tactic to spread their product around the world.
They paid ships' captains to promote their spirit around the world, effectively making them agents for Johnnie Walker, and the square bottle design was adopted to make the whisky easier to store in the holds of freighters as it was taken to the four corners of the globe.
After the Cardhu distillery was purchased to ensure consistency of quality in the blended product, the iconic Johnnie Walker Red Label and Black Label were introduced in the early years of the 20th century, along with the whisky's familiar 'striding man' logo and its unique slanted bottle label.
John Walker & Sons became part of the Distillers Company in 1925 and subsequently part of the Guinness group following a takeover in the 1980s.
Guinness later merged with Grand Metropolitan form Diageo, the world's largest producer of spirits, in 1997.
In the mid-1950s Johnnie Walker became the world's best-selling whisky and has been the top Scotch brand ever since.
It's been a consistent favourite with some of whisky's most famous fans. Winston Churchill was said to be an enthusiast, as was Vanity Fair essayist Christopher Hitchens.
It's said that during the filming of Carry On Again Doctor, legendary comedy actor Sid James insisted on an entire cupboard being filled with Johnnie Walker Red Label for one scene.
And if you look closely at many of the drinking scenes in The Sopranos, you'll see a bottle of Black Label is never far from Tony's glass.
A number of variants have been created in more recent years, among them Johnnie Walker Blue Label, the most prestigious blend, which was introduced in 1992 and retails for upwards of £130 a bottle. "Only very special casks of Cardhu are set aside for Blue Label," says Andrew. "We might produce perhaps one every 18 months."
Special editions are another recent feature of the brand. Recent bottlings include 'Jane Walker', a female-friendly Black Label variant and the upcoming 'White Walker' limited edition which marks the final season of TV hit Game of Thrones.
The recent record growth in Scottish tourism, coupled with Johnnie Walker's position as a leading global brand, has prompted Diageo to announce the investment of £150m over three years to create a Johnnie Walker visitor experience that will coincide with the 200th anniversary of the brand in 2020. The move follows the enormous success of the Guinness Storehouse in Dublin, another Diageo project, which has since become the Republic's number one paid visitor attraction.
The plans for the Johnnie Walker Experience are still being drawn up, but the company is looking at high profile sites in Edinburgh to locate the central visitor attraction, which will tell the story of the brand and how it came to be a worldwide hit.
Expected to play a key role in the creation of the Johnnie Walker Experience is the Diageo Archive, a central repository of documents, files and products that charts the history of Diageo's diverse drinks portfolio.
Stored here is a sample of every Diageo product, including the oldest-known bottle of Walker's Old Highland Blend from the early 20th century, which has a preserved snake coiled among the amber liquid.
The archive also contains the bill of sale for Walker's farm which provided the capital to start his world-spanning business and a host of other memorabilia, ranging from early magazine adverts and promotional material to account books and production ledgers.
It's highly likely that much of this fascinating material will be reproduced or displayed in the new visitor centre in Edinburgh.
The centre will also be linked to four other Scottish distilleries, representing the four main areas of whisky production - Highlands, Islands, Lowlands and Speyside - each with their own unique flavour characteristics.
The key highland distillery will be Clynelish, the island distillery will be Caol Ila on Islay, the lowland distillery will be Glenkinchie, about an hour's drive from Edinburgh, and the Speyside distillery will, of course, be Cardhu.
"Diageo has made a huge investment of over £1bn in Scottish distilling in the past six years," says Andrew, "and the company is reviving two old distilleries, Brora and Port Ellen, to expand even further. It really is a boom time for the whisky industry in Scotland."
The plans for the Cardhu element of the Johnnie Walker Experience have still to be announced, but it's expected that the distillery's already excellent visitor facilities will be upgraded even further.
As has always been the case in its long association with Johnnie Walker, Andrew Millsopp insists: "Cardhu will play its part."