Just about getting by with Leeds United, he was, in a gruff sort of way, more mature even then than the average professional footballer, but he could be as childishly mischievous as any of them.
That first came to mind personally on a coaching course at Lilleshall where we struck up what could be described loosely as an alliance. In other words we downed a few pints - he was buying in those days - and tried to imagine questions that might crop up in the examination.
Walter Winterbottom did not select Charlton for the England team but in his other role as director of coaching he identified a bright mind for the game. The big Geordie would make a fine coach, no doubt about it.
Late one night, I asked Charlton clumsily what he intended doing with the rest of his life. He understood the implication exactly. Almost 10 years a professional and not much to show for it. ''Haven't got a flaming clue,'' he growled, the frustration, some of it self-inflicted, coming out in him.
The conversation that changed Charlton's life took place at Elland Road a while after Don Revie was appointed manager of Leeds and is quite famous in the lore of football. Revie felt that his transfer-listed centre-half, even at close to 30, was still capable of representing England, but only if he was willing to conform. As Johnny Giles would later put it, Charlton was not always right but in his own mind he was never wrong.
The subsequent transformation brought 35 caps, a World Cup winners' medal, domestic and international club honours, including Footballer of the Year.
If Charlton's appointment as manager of Middlesbrough was a natural progression, it had a characteristically confused beginning. ''When I got to the hotel Jack suggested as a meeting place, it was a pile of rubble,'' said the club's vice-chairman, Neil Phillips, who was physician to the England team.
One of the stipulations Charlton laid down was that he would not attend board meetings. ''Only Jack could have got away with that ,'' Phillips added. ''He would do the job his way or not at all.''
It was, more or less, the way Charlton continued to go about things. While there was a river to fish, management was never likely to interrupt his sleep or cause ulcers but he was shrewder in planning and application than many imagined. Charlton's teams did not gain many marks for artistic impression but they were always damned difficult to play against.
Ten years ago, Charlton seemed to be at the end of his tether. Irritated by the demands of players he was attempting to sign for Newcastle and barracked by the club's supporters, he walked away from the game.
Hearing news of it while on holiday, I called him. ''Not the wisest thing you've done,'' I said. ''Sod 'em,'' he replied.
That an English hero should become so popular on historically alien ground is a phenomenon best explained by Charlton's instinct for being nothing but himself, a characteristic that appeals mightily to the Celtic nature.
Since the policy Charlton advanced owed nothing to romantic idealism, he was never in trouble-free waters but until recently most of his detractors were held at bay by public opinion.
A criticism lately is that Charlton has not made the best use of available talent and that the selection of four full-backs for last week's play- off against the Netherlands was irrefutable proof of deep-rooted conservatism.
However, to suggest, as the former international, Eamon Dunphy did, that Charlton laid a dead hand on brilliant players takes some understanding. With one or two exceptions, they were never better than average. What can be suspected is that changes in the government of Irish football made it more difficult for Charlton to maintain his independence.
At 60, a return to club management is not an option and he is beginning to grow weary of the after-dinner circuit. Well off, he may simply settle for retirement.
What can be imagined is his response to remarks made at yesterday's meeting with officials of the Football Association of Ireland in Dublin. Probably, it was something like: ''Gentlemen, you can shove it.''