Just a few miles north-east of downtown Dallas is a 1000-acre lake known as White Rock, surrounded by large and expensive houses. But the priciest of them all is Mt Vernon, a magnificent white-pillared colonial mansion whose manicured lawn trails off towards the water. It was built in the Thirties by a man called Haroldson Lafayette Hunt, known as HL. A gambler-turned-oil-prospector, Hunt was asked in his eighties by a TV interviewer whether he really earned a million dollars a week. “I would starve to death with an income of a million dollars a week,” he replied.

The New York Times described HL, who died in 1974, as an “unconventional renegade who possessed the money to pursue his whims”, and the in-fighting of the Hunt family as “entertaining as any soap opera”. Hunt has frequently been called “the real-life JR Ewing”, and with good reason.

Mt Vernon is now up for sale for $29.5million (£18.8 million) — the most expensive house on the city’s property market. Just as the house dwarfs the real Southfork Ranch, 20 miles north of here (where the original Dallas was filmed), the Hunts’ story – a Texan-sized drama that runs the gamut of bigamy, oil, Middle East dictators, politics, sibling rivalry, billion-dollar fortunes and equally enormous lawsuits – is considerably crazier than the fiction of the Ewing clan. And that includes not just the original series but the revamp, which is due to begin on Channel Five in September. As Larry Hagman, the actor who plays JR Ewing in both, once said: “It makes Dallas look like milquetoast.”

In the Twenties, old man HL bought a half-an-acre oil lease in Arkansas with borrowed money, drilled his first well and struck black gold. By the end of the Twenties, he had more than 100 wells. But it was something that became known as the “Dad Joiner deal” that would provide both the money and the drama to come.

The major oil companies didn’t think there was any oil in Rusk County, 130 miles east of Dallas, but an independent oil speculator named Columbus “Dad” Joiner continued to prospect there, and in order to keep drilling when wells were dry, he sold far more stock certificates than he could honour. In September 1930, his Daisy Bradford No 3 well blew a gusher in front of 5,000 cheering onlookers, but two months later he was forced to sell all his holdings (including about 5,500 leased acres) to HL Hunt for $1.3million. The transaction offered Joiner a way out of his legal mess and HL a ticket to unimaginable wealth.

Daisy Bradford No 3 turned out to be the first producing well in what at the time was the world’s largest oilfield. To date, the east Texas field has produced more than five billion barrels and is still producing. And HL Hunt became the largest independent oil operator in that field.

As the journalist John Bloom wrote in Dallas’s D magazine, there are “unmistakable parallels” between the Ewings and the Hunt family. The first episode of the original series, after all, began with a crime: Digger Barnes, an alcoholic, is shown to have been cheated out of his share of an oilfield by Jock Ewing, who then founds Ewing Oil. Bloom goes on: “The year of this alleged trickery: 1930. So it sounds a whole lot like the contract that H L Hunt got Dad Joiner to sign four hours after oil was discovered in Rusk County.”

Bloom adds that in the Ewings’ world “babies are currency, like bloodstock, so their paternity always has to be proven”, but that J R “never had anything like HL Hunt’s 'secret’ family”. In fact, HL had three families that he kept hidden from each other; a total of 14 children by three different women. There was his wife Lyda Bunker and their six offspring. Then, when Lyda died of a stroke in 1955, HL married Ruth, a former Hunt Oil secretary, with whom he had already secretly sired four children.

HL’s infidelity was tough enough on both sets of children, but it wasn’t until some time later that they would learn that Hunt had also married a woman named Frania Tye and fathered four children by her, too. Tye later sued the Hunt estate, telling a court HL offered her $1million in 1942 to sign a statement saying she’d never married him so he wouldn’t be outed as a bigamist.

As Harry Hurt, author of Texas Rich, a book about the Hunt dynasty, puts it, HL “created a three-branched family tree whose numbers were destined to feud with each other long after he was gone”. Hurt tells me the fact HL wanted to have children by his secret wives rather than hide or disavow them was testament to the high opinion he had of himself. “He thought he was doing the rest of the world a favour by spreading his genetic content.”

HL became, at one point at least, the world’s richest man. But he would also bring his lunch to work in a paper bag and had a fondness for cheap suits. He was a health crank, inventing a peculiar form of exercise he termed “creeping” which involved crawling along the floor on all fours, and manufacturing his own brand of herbal diet pills.

Eccentric though he may have been, the old man was also shrewd. He set up trusts for his 14 children, and as a Hunt insider told me, “for that kind of wealth to be maintained through generations is incredible. You’d find it hard to see it duplicated anywhere. And I defy you to show me any of the heirs who is poor.”

By the Sixties, some of HL’s children by his first wife Lyda were making names for themselves too, and, like their father, not always for the right reasons. Herbert bought up 6,000 acres of north Dallas, which made his particular family trust hundreds of millions of dollars. His brother Nelson, known by his middle name Bunker, chased oil concessions in Libya and of the concessions he won, one turned out to be the first strike in the biggest oilfield in Africa.

Sarir was three times the size of the east Texas field that made Bunker’s father rich, and although he sold half his interest in it to BP, it still ensured he was worth an estimated $8 billion on paper, making him richer than any other private individual in the world – including his father. But in 1969, Colonel Gaddafi deposed King Idris in a coup and nationalised the oil industry. Bunker’s adventure was over.

In the Seventies, with the US economy in turmoil, Bunker and his brother Herbert took out a loan so they could begin investing in silver in an attempt to corner the market. At one point they are believed to have held a third of the world’s silver supply. According to a source close to the Hunts, “Bunker and Herbert bought so much, they had to literally hire ranch hands with guns to take delivery of it.” Then the price began to fall, dropping more than 50 per cent in just four days, and the Hunt brothers couldn’t pay their debts. The market was sent into panic, culminating on March 27 1980 in “Silver Thursday”, the day that saw the largest drop in the price of silver. The Hunts filed for bankruptcy.

Lyda and HL’s daughter Caroline used her own trust to invest in hotels. Her Rosewood Hotels & Resorts is now a $300 million global empire. As for Lamar, HL’s other son by Lyda, he co-founded the American Football League in 1959 and was credited with coining the term “Superbowl”. Lamar also made a failed attempt at turning San Francisco’s Alcatraz island into a shopping mall and space museum.

HL’s wife Ruth and their four offspring seem to have, as Hurt says, “more of a religious/philanthropic impulse than the older group”. Of the three girls, June, now 67, is CEO of a Christian radio ministry; Helen, 62, is founder of a philanthropic endowment designed to advance the “spiritual empowerment of women”; and Swanee became US ambassador to Austria under President Bill Clinton and now runs her own philanthropic fund, Hunt Alternatives.

HL and Ruth also had a son, Ray, who, along with his three sisters, inherited most of the Hunt Oil Company. Today, he is president and CEO of Hunt Consolidated, the umbrella organisation which owns Hunt Oil, and this year Forbes estimated his net worth at around $5 billion (£3.2 billion). Unlike his wayward father, Ray tends to stay below the media radar – as much as he can help it, anyway.

For years, Ray and his family lived in a modest home before moving to a $2.5 million house on the estate of an exclusive Dallas country club. “It’s nice but not terribly ostentatious,” someone close to the Hunt family tells me.

The Hunt insider says that for the first 15 years of his life, “Ray was just seen as Bunker and Lamar’s bastard brother”, but that he has arguably proved a more savvy businessman. Ray Hunt is friends with former presidents George Bush Sr and Jr and, controversially, won the first permit to explore for oil in Kurdistan in 2010.

Ray and his siblings have also remained on much better terms with each other than the descendants of HL’s older children from his marriage with Lyda. After HL’s daughter, Margaret, died in 2007 a ferocious legal battle began between her grandson, Albert Hill III, known as “Al Three”, and the rest of the family over the management of the trust fund and Hunt Petroleum Corporation, an oil and gas company separate from Hunt Oil.

As a college student, wrote one Hunt-watcher, Al III “double-majored in partying and crashing cars”. He had already wrecked two sports cars and a motorcycle before driving his girlfriend’s Toyota into the wall of a house at 65 miles an hour. Nobody died, but as a result, Al III spent 30 days in rehab, gave up drinking, and found God.

Today, he is married to Erin Nance, a former Miss Georgia and Miss USA contestant. In 2007, the couple spent almost $500,000 on holidays alone. Al III’s father, Al Jr – a former tennis pro who dated Bond girls and was temporarily paralysed in 2003 after falling off his balcony – once claimed that he tried to stop the flow of money but couldn’t change his son’s spending habits.

According to Candy Evans, who blogs about the Dallas property market, in mid-2011 Al III and Nance were indicted for mortgage fraud, and within a few months had up and moved to Atlanta – into the most expensive home ever sold in the city. The lawsuit was settled in 2010, but it’s thought the two Als still aren’t speaking to this day.

No member of the Hunt clan has lived at Mt Vernon for years. It’s being sold by a couple who made their fortune in property. I was given a tour by Allie Beth Allman, broker to Dallas’s rich and famous. It’s slightly larger than first US president George Washington’s home in Virginia, after which Mt Vernon is modelled and named. The tennis court and pool are still there – one of the first outdoor pools to be built in a private residence, which HL had dredged by mule. There’s also a fully fitted bowling alley with soda fountain and beer on tap, but that’s a recent addition. A bowling alley would have been too ostentatious for old HL.

This article also appeared in SEVEN magazine, free with the Sunday Telegraph. Follow SEVEN on Twitter @TelegraphSeven