Frank Keogh
BBC Sport at Aintree

Despite both being well backed, trainer Jonjo O'Neill concedes his pair Shutthefrontdoor and Holywell will not be aided by the rain.

"The fences will seem a bit bigger to Holywell," said O'Neill of the horse, who prefers good, drier ground.

Image source, PA

This time last year Shutthefrontdoor was the bearer of 11st 2lbs, but a tonne more sentimental hope and cash.

He went off as favourite, but could not deliver champion jockey AP McCoy a fairytale farewell, finishing only fifth.

His form has been modest since but the late money seems to have spotted something it likes. His odds have come in plenty over the last 24 hours.

Barry Geraghty is on board today.

A guide to all the Grand National runners in our pinstickers' guide.

Image source, Getty Images

Nineteen times, Richard Johnson has started the Grand National.

And 19 times he has watched some other fella spraying the bubbles and slapping high fives in the winners' enclosure.

It is the longest winless run of any jockey ever in the race.

Can he break his duck this year? His hope is Kruzhlinin, who was a well-beaten 10th behind Pineau De Re in 2014 but has switched to trainer Philip Hobbs since then.

Image source, Rex Features

You say Holy-well, I say Holly-well.

We all can agree it has a big chance.

The stand-out win of his career was at this course when in the 2014 Aintree novice chase he left Don Cossack - last month's Gold Cup winner - far behind.

Trainer Jonjo O'Neill triumphed six years ago with Don't Push It ridden by AP McCoy. 

A guide to all the runners in our pinstickers' guide.

The jockeys gather for a pre-race group photo.

A quick head count reveals we have only 38, rather than the required 39.

Here is the missing man. Will Kennedy, who will ride Katenko, is just in time to make the frame.

Image source, Rex Features

"You can't park that there, mate."

Someone has arrived in style on the course.

Image source, Getty Images

Like The Chair, the Water Jump is only tackled once by the field.

The fence is a tiddler, but this is a long jump - rather than high jump - of an obstacle.

The runners are also attempting to clear a six-foot wide stretch of water on the landing side.

An open goal for the railside snappers who will be lurking to get some of the best photos of the day.

Image source, Getty Images

The Chair is the 15th and tallest fence - on take-off side at least - on the National course at five foot two inches. And there is a six-foot ditch to clear before you get to the spruce as well.

It is the site of the only human fatality in the race. 

In 1862 jockey Joseph Wynne was badly injured after falling at The Chair, dying a few hours later.

It is so-called because of its position alongside the 'seat' erected for the 'distance' judge.

Poor spelling. Good horse.

Last seen leaving The Druid's Nephew choking on 10 lengths of fumes in March's Grimthorpe Chase, The Last Samuri heads out at an easy-going 10st 8lbs.

Trainer Kim Bailey was the man behind Mr Frisk's thrilling triumph in 1990. David Bass is on board.

Image source, PA

Hold the phone. 

We have have a new favourite with The Last Samuri shortening in to 9-1.

Time to have a detailed gander.

If Many Clouds comes home in front today it will end a six-year wait for a favourite to win. The last was 10-1 chance Don't Push It in 2010.

Rough Quest was the first winning favourite in 14 years when he scored at 7-1 in 1996 and market leader Earth Summit struck just two years later at the same odds. Golden Miller started the shortest-priced favourite ever in 1935 at 2-1 but failed to complete the course. 

And this is how Leighton Aspell and Many Clouds did the business last year, courtesy of an on-board camera.

Image source, PA

That? 

That will be the sound of shattering vinyl if 2015 winner Many Clouds comes home and breaks all sorts of records.

He would be the first horse since Red Rum in 1973 and 1974 to win back-to-back runnings of the Grand National.

Jockey Leighton Aspell, who also rode Pineau De Re to victory in 2014, would be the first jockey to win three Nationals in a row.

Owner Trevor Hemmings would be the first owner to win the race four times, after previous successes with Hedgehunter (2005) and Ballabriggs (2011).

A commanding 10-lengths win over Unioniste at Kelso in March sent his odds tumbling and he is set to go off as favourite.

Full rundown of the field with our pinstickers' guide.

Time to run the rule over the contenders.

And no better place to start than the top of the betting...

Aintree is the red dot in the centre of all that rainfall...

Image source, netweather.tv

But for the next hour or so it is all about the biggest test in horse racing.

And this year it is looking like a particularly gruelling examination of nerve, jumping, stamina and horsemanship.

The going is soft and James Reveley - the winning jockey in the last race - suggests that it is "borderline heavy".

On this sport-packed Saturday it isn't just racing we'll be keeping you up to date on.

If you fly 3981 miles west of Aintree you'll be in Augusta, where the third round of The Masters is getting under way, with Rory McIlroy and Jordan Spieth going head to head later.

Click here to follow all the action on our live text commentary and also watch featured groups live online.

Image source, BBC Sport