So how did this 28-year-old man come, as police believe, to hang himself at the weekend in a wood in Perthshire between his mother's home and his own? It is a question his family pondered on Sunday, as they prayed at the Church of Nazarene, the church near Perth where Jonathan was married six years ago and whose strict Wesleyian code continues to shape the entire Gloag family, despite the gold jewellery, the fast cars and the Highland castle which Ann Gloag now enjoys as a result of her success.
The plain answer to the question, as with so many men of Jonathan Gloag's age, seems to be a long-term depressive illness, a tragic and often inexplicable condition which wealth and treatment appears to have alleviated only temporarily. Additionally, his life cannot be separated from the family trauma which has accompanied his family's extraordinary business success.
First there is the sheer size of the wealth accumulated in less than 20 years since a tough, business-minded family had the good fortune of finding its feet at just the moment when a Conservative government was delighted to sell off state bus companies for a song.
"They came from being the children of a bus driver to being Scotland's premier family," says Christian Wolmar, the transport writer, who last year published Stagecoach - A Rags to Riches Story At the Frontiers of Capitalism (Orion, pounds 18.99).
"That must have put an enormous stress on the family. And the incredible work ethic that their religious upbringing gave them also must have added its own strains. When Stagecoach was starting up Ann Gloag worked incredibly hard.
"Then there is the difficulty that the sons of those with money have in establishing themselves. You cannot just go and find a job, because it looks meaningless when you are going to inherit all that money. All in all, Jonathan may have had a hard time of it."
Ann Gloag, now 56, did what she could to support her son. She did not spoil him with wealth during a period when she has gained a taste for the good things in life. Her Bentley, complete with the pounds 50,000 number plate "1 ANN", used to belong to the Princess Royal. In 1995, she bought one of Scotland's most historic homes - Beaufort Castle, near Inverness, seat of the Clan Fraser for more than 500 years. In contrast, when Jonathan attended university, she was proud to declare that she gave him only basic living expenses and he drove a bus at weekends to make ends meet.
Likewise, although she paid for Jonathan's family home, near where he died, it was not, at pounds 450,000, an extravagance for a man who was destined to inherit a sizeable chunk of her estimated pounds 850m fortune.
Ann Gloag is not a mumsy woman. "As tough as nails" is the usual phrase accompanying her name. But she has a soft spot. She is a loving mother by all accounts. She supports international aid charities and has adopted a Kenyan boy, Peter, now aged 15. Most of all, she values her family. "To me," she once said, "it is everything. Family life is great. If I thought money would spoil it, I would throw it all away."
Yet the tragedy is that business success and money for Mrs Gloag has been closely entwined with, perhaps even dependent upon, family failure. Stagecoach was originally established by Mrs Gloag, her younger brother Brian Souter and Jonathan's father, Robin Gloag, who married Ann when she was 18. "Unfortunately, Robin was a simple fellow," says Wolmar.
"He was happier underneath the coach repairing it, than running it. It got to the point where Ann and Brian felt Robin had to go."
Eventually, with the marriage falling apart, Robin was squeezed out, divorced, bought out and, in the business world, humiliated. When he set up a rival firm called Highwayman in competition, Stagecoach stopped charging its passengers, Robin went bust and Stagecoach snapped up his company. Ann Gloag has since recalled her ruthlessness, for which she is famous in the City: "It makes me sound awful, but I can't deny it is the truth."
Jonathan helped to put the family back together again. Aged just 11 and starting secondary school when his parents split up, he became close friends with Sarah McCleary, whose father David was the organist at the local Church of the Nazarene and the owner of a local laundrette.
Jonathan and Sarah introduced Ann to David, a widower with two other children by his first marriage. Romance blossomed between the older couple, who eventually married in 1990. David had proposed to Ann while mending her dishwasher. After the wedding ceremony the couple and their children travelled aboard a 1922 Leyland open-topped trolley for a four-course feast at the home they had established together - Balcraig House, a former hotel which is close to Perth.
Suddenly, the younger couple found themselves stepbrother and stepsister, with Jonathan having to ask his stepfather's permission to go out with Sarah, four years his junior. In an intriguing echo of Ann's close business relationship with her brother Brian, Jonathan and Sarah were married quietly in 1993, when Sarah was 18. They have three children, the oldest aged just four.
However, the damage to the relationship between the humiliated Robin Gloag and his son never seems to have been repaired. At his farmhouse in Incture, Perthshire, Mr Gloag heard about Jonathan's death from the police, not his own family.
"No one from the family had contacted me, but that's not a surprise to me. It is well-known that we don't speak," he said. Of the acrimonious divorce from Ann Gloag, he added: "It all became very difficult when we split up and I have not really been close to Jonathan since he was a boy. We didn't really speak at all and it was the same with everyone involved at Stagecoach."
It does not sound like a happy set-up for a boy, later a man, who was attempting to cope with how to follow in the footsteps of a hugely successful mother. His faltering steps are recorded: he worked for a while in the family firm, then trained as a chef, and most recently worked as an estates manager. And he was a father of three young children. An excellent record of achievement for a young man of 28, whose grandparents eked out a living. But it was not enough, apparently, to prevent depression pushing Jonathan Gloag, a man with a great fortune lying ahead of him, into a lonely and premature death.Reuse content