Beyond a long and distinguished playing career, the subsequent unfulfilled sorties into club management at Middlesbrough, Sheffield Wednesday and Newcastle, there is the phenomenon of Charlton's sainthood, his emergence as the greatest and most unlikely hero in the history of Irish sport.
If Charlton's appointment ahead of the former Liverpool manager, Bob Paisley, was seen by some to be a mistake (it was rumoured that a vote for Paisley typically ended up in the wrong envelope) he quickly proved to be more quirky than the Irish themselves, disarming prejudice with blarney, especially the statement, 'I'm not an Englishman, I'm a Geordie.'
To an extent Charlton is a prisoner of his candour. The rules, he once explained to interrogators, were simple but absolute. 'I don't answer any double-barrelled questions,' he said. 'There's no point in asking those questions because I'm not going to answer them, and anybody who says I ever will or ever did is a liar.' Once, a particularly virulent critic was invited to sort things out in the most obvious manner imaginable.
With the essentially erratic Republic team, he first had to oppose romance with reality, seeking out words and phrases to prove that he was harder than any of his former team-mates at Leeds and in the England squads can remember. It was as though the discovery of some kindness would undo it all, the revelation that he suffered bouts of civility and compassion would destroy the dream and transform him suddenly into something pallid.
Talk is another kind of mask. Charlton beats away questions with other questions and holds people off with blunt pronouncements, a trick that the England manager, Graham Taylor, has never learned.
Charlton's success, achieved in part through the brazen recruitment of tenuously linked mercenaries, irritates in some quarters, even in Dublin. His playing method, relentlessly direct, if recently more refined, has seldom rated better than zero for artistic impression.
Former internationalists have referred to his methods darkly. 'I don't think I'll ever be happy with Jack's way of doing things,' one said. 'The long ball. The idea that we can be represented by people who don't know the words of our anthem. It smacks of expediency. Profit before honour, all that is wrong with modern sport.'
A far more popular and convincing point of view is that Charlton raised football in the Republic from the dead, qualification for the European Championship finals in 1988 and the World Cup finals two years later not only spreading interest on a grand scale but bringing financial stability.
Until last month, no one auditing Charlton's progress would have bet against him qualifying the Republic for next summer's World Cup finals in the United States. It was all over bar the shouting. Trips were being booked, relatives had been alerted. Then came the 3-0 defeat by Spain at Lansdowne Road that threw everything forward to tonight's pressure match against Northern Ireland at Windsor Park, Belfast.
Charlton makes phrases, strong, often memorable ones. 'I've never been in a game with so much on it,' he said. 'We're not playing against the best team in the world, but the circumstances, the security and everything, are bound to make things difficult.'
Spain's victory last month left him in a state of shock, confidence dented. 'It was the way we lost that was so disappointing,' he said. 'I'm never complacent and knew that Spain are a good team with some extremely promising young players. But nobody enjoys playing us in Dublin, and I felt that if we could get at them quickly things would go our way.'
Instead, with barely 20 mintues played, the Irish found themselves two down and chasing the game. When Spain scored again, it was an impossible task. 'We gave away silly goals,' Charlton said, 'didn't give ourselves a chance.'
Another truth is that players who have performed importantly within the shape of Charlton's controversial strategy, accommodating a purpose that probably is alien to their instincts, can no longer be relied upon for an effective contribution.
Sport tells anyone who watches intelligently what the process of ageing does to strong men. Has the challenge come too late for some of the Republic's heroes? Will Northern Ireland and their astute manager, Billy Bingham, finally put paid to the celebrations?
Defeat would leave the Republic stunned. 'It comes down to one simple truth,' Charlton said. 'We are playing for a place in the World Cup finals and all that goes with it. Not just the glory and the profit, but what our presence in the United States would mean to the Irish people. I think we are good enough and if we perform at our best we should be all right.'
Something like that will be heard tonight in the Republic's dressing- room.
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