That image of one of the greatest and toughest managers in the game's history - many would say the greatest and toughest of them all - being woken by the memory of his lost mate is a deeply poignant moment in a film that's regularly moving, occasionally hilarious. The famous tunnel scene in which Smith plays with Chick Young as a cat does a mouse is worth a documentary of its own - and a touch surreal.

It's been just over two months since Smith passed away, since he became the late Walter Smith, since his legions of admirers said their goodbyes. No doubt many of his family and friends are still firmly rooted in the no-man's land of grieving - knowing that he's gone but still half expecting him to be on the end of the phone or to walk through the door. You can't have such a massive impact in life without leaving such a giant void in death.

The essence of what made Smith a great manager shines through in the documentary. He was a people person first and foremost. He learned about coaching in his days as Dundee United assistant under Jim McLean at Tannadice, but his ability to manage those around him and get the best out of them was instinctive.

He had a natural ability to inspire, sometimes without even having to open his mouth. So many of his players have said it - they didn't want to let him down, they would have run through a brick wall for him.

Why? Because of his presence, his aura. When asked to explain the presence and the aura, many of them struggle. He just had it, they'll tell you. Whatever 'it' is - an indefinable something, hard to explain, maybe it was just an essential honesty and goodness. Or maybe just a part of it.

In his character he also had an intense quality, another aspect of what made him so successful and so fascinating. Either a hammed-up ferocity or the real thing, it was hard sometimes to tell the difference and nobody on the end of one of his scowls - or worse - was ever minded to query whether he was serious or just at it.

The scene with Chick, a great friend of Smith's, is the ultimate example. Filmed the day after a bruising Rangers loss to AEK Athens in 1994, it's a sweary tour de force. This was not a shouty rant, it was a controlled evisceration elevated to an art form. You can feel for the bold Chick, while at the same time laughing uproariously at his dismal plight.

Once Chick suggests Smith's recent big-name signings have been failures in Europe, it sets the scene for arguably the funniest thing ever recorded in the history of the Scottish game. You could never tire of watching it.

"You saying that [Basile] Boli and [Brian] Laudrup can't play in Europe?" Smith says before an expletive-filled rant that culminates in him suggesting the intrepid Young was having a "horrendous" day.

Playing the scene out in full in the documentary was a good idea because it captured another layer of Smith's personality. We had the workaday football player, the hugely successful and idolised football manager, the family man and the friend.

What we had here was the mischievous soul, the performer, the wind-up artist and the comic with the most perfect timing. He later said he wished he'd never behaved that way in the interview because his grandkids had seen it online and asked why he was swearing at the nice man.

Significant figures from every stage of his football story are interviewed in the documentary. From Maurice Malpas at Dundee United, to Sir David Murray, Graeme Souness, Archie Knox, Brian Laudrup, Richard Gough and others in his first spell at Rangers, to Wayne Rooney at Everton, to Ferguson at Manchester United, to James McFadden and Scotland and Davie Weir from his remarkable return to Ibrox and that run to the Uefa Cup final in 2008.

The day after that loss to Zenit St Petersburg in Manchester, the horrible news of Tommy Burns' death was announced. Smith was a pallbearer at his friend's funeral.

Burns' son, Michael, speaks about their friendship, not through the prism of football but as two good men who just enjoyed each other's company and who made each other laugh. They elevated themselves above the cynicism, bitterness and poison that can exist between extreme elements among the support of their clubs. They did it to their dying day.

The cornerstone of the piece is a 2016 interview with Smith himself for the BBC series Scotland's Game. Smith spoke for almost an hour and most of the footage has been never been seen before, until now.

"Football," he says, "is more than a game, it's a passion."

And Smith lived it to the full. You can't look at him in the documentary, glowing with health, and not feel the man was cruelly robbed of many great years. Gone at 73, a desperate loss. All that's left are memories. So many, many memories of a wonderful life.