There's no other race like it. Nothing captivates or divides public opinion and imagination like it. And on Saturday at 16.15 BST, over 500 million people will be tuning in to the greatest show on earth: the 168th running of the Grand National.

For die-hard race-goers, the Grand National is the pinnacle, El Gordo, the one they all want to win. It is the toughest test of mental and physical fitness for both horse and jockey, as they dispute 4 miles and 3 ¼ furlongs, jump an unparalleled 30 fences over two circuits, and jostle for position in a field of 39.

For the fair-weather fan, the National is the one where even the least likely gambler will have a flutter, where most work places will run a sweepstake, and where people who would never watch sport, let alone racing, will make sure they are at home in front of the television to watch the spectacle unfold.

Safety First

But the world's most famous steeplechase is also the most contentious, and this year's running takes place following £1.5m worth of alterations after a total of four horses were killed in 2011 and 2012. Obstacles that were previously wooden have now been replaced with a more forgiving plastic core, and landing sides have been also been modified. Officials claim that these modifications strike the right balance between safety and the risks we realistically expect in a jumps race.

It certainly seems that these changes have been successful, as the last two runnings have seen all horses and riders return safe and sound, if not a little tired.

This year, 150,000 people will descend upon the famous site at Aintree where Red Rum made history with a record-breaking three National wins to his name. This year, all eyes will be on another record-breaker, as AP McCoy, surely the greatest jump jockey of all time, seeks to add a second National win to his name in his final season in the saddle.

The 19-times champion jockey won his last - and only - National in 2010, when he ended his Aintree jinx at the 15th time of asking. That year, he was on board 10-1 joint-favourite 'Don't Push It', in what was also a first win in the race for trainer Jonjo O'Neill and owner JP McManus. Until that victory, McCoy had ridden over 3000 winners, but the National was the one that continued to elude him.

History at Stake

McCoy has claimed that if he wins his second Grand National this weekend, he will retire on the spot. It would certainly be a fitting way for arguably the greatest-ever jockey to call time on his peerless career. If not, there will be a few more rides for him until the jumps season finishes in April, when he will conclude his career at Sandown and be formally crowned Champion Jockey for the 20th successive year. McCoy joins the O'Neill-McManus partnership again on Saturday with 'Shutthefrontdoor' - a horse that bookmakers believe will be sent off the shortest-priced favourite since the legendary Red Rum went off at 7-2 in 1975. The favourite was beaten into second that year by L'Escargot, who triumphed by 15 lengths, but connections here are confident their eight-year-old will go one better than that.

Sightings of 'Shutthefrontdoor' have been rare since he won the Irish National in 2014. Indeed, the horse has only made one racecourse appearance since then - albeit a successful one - with a win in Carlisle in November. Reports coming from Jackdaws Castle suggest the gelding is in the form of his life, and a wind operation in the intervening months means we could yet see the horse reach another gear. And after all, the National has never been averse to fairy-tale winners.

McCoy the Legend

Such is the will for AP to win the National at his final time of asking, that a giant image of 'The Champ' has been beamed onto Liverpool's iconic Royal Liver Building ahead of the three-day race meeting.

The accompanying words "the greatest jockey", "the greatest race" and the hashtag #GOODLUCKAP, summarise just how influential this man has been on the sport and how keenly his absence will be felt. But not only that; AP's image being beamed across Merseyside also demonstrates just how far the Grand National transcends horse racing: it is far more than just a horse race. It is an institution.