Enron was formed in 1985 following a merger between Houston Natural Gas Company and Omaha-based InterNorth Incorporated. Following the merger, Kenneth Lay, who had been the chief executive officer (CEO) of Houston Natural Gas, became Enron's CEO and chairman. Lay quickly rebranded Enron into an energy trader and supplier.

Deregulation of the energy markets allowed companies to place bets on future prices, and Enron was poised to take advantage. In 1990, Lay created the Enron Finance Corporation and appointed Jeffrey Skilling, whose work as a McKinsey & Company consultant had impressed Lay, to head the new corporation. Skilling was then one of the youngest partners at McKinsey.

Skilling joined Enron at an auspicious time. The era's minimal regulatory environment allowed Enron to flourish. At the end of the 1990s, the dot-com bubble was in full swing, and the Nasdaq hit 5,000. Revolutionary internet stocks were being valued at preposterous levels and, consequently, most investors and regulators simply accepted spiking share prices as the new normal.

One of Skilling's early contributions was to transition Enron's accounting from a traditional historical cost accounting method to mark-to-market (MTM) accounting method, for which the company received official SEC approval in 1992.

MTM is a measure of the fair value of accounts that can change over time, such as assets and liabilities. Mark-to-market aims to provide a realistic appraisal of an institution's or company's current financial situation, and it is a legitimate and widely used practice. However, in some cases, the method can be manipulated, since MTM is not based on "actual" cost but on "fair value," which is harder to pin down. Some believe MTM was the beginning of the end for Enron as it essentially permitted the organization to log estimated profits as actual profits.

Enron created Enron Online (EOL) in October 1999, an electronic trading website that focused on commodities. Enron was the counterparty to every transaction on EOL; it was either the buyer or the seller. To entice participants and trading partners, Enron offered its reputation, credit, and expertise in the energy sector. Enron was praised for its expansions and ambitious projects, and it was named "America's Most Innovative Company" by Fortune for six consecutive years between 1996 and 2001.

One of the many unwitting players in the Enron scandal was Blockbuster, the former juggernaut video rental chain. In July 2000, Enron Broadband Services and Blockbuster entered a partnership to enter the burgeoning VOD market.

The VOD market was a sensible pick, but Enron started logging expected earnings based on the expected growth of the VOD market, which vastly inflated the numbers.

By mid-2000, EOL was executing nearly $350 billion in trades. When the dot-com bubble began to burst, Enron decided to build high-speed broadband telecom networks. Hundreds of millions of dollars were spent on this project, but the company ended up realizing almost no return.

When the recession hit in 2000, Enron had significant exposure to the most volatile parts of the market. As a result, many trusting investors and creditors found themselves on the losing end of a vanishing market cap.

By the fall of 2000, Enron was starting to crumble under its own weight. CEO Jeffrey Skilling hid the financial losses of the trading business and other operations of the company using mark-to-market accounting. This technique measures the value of a security based on its current market value instead of its book value. This can work well when trading securities, but it can be disastrous for actual businesses.

In Enron's case, the company would build an asset, such as a power plant, and immediately claim the projected profit on its books, even though the company had not made one dime from the asset. If the revenue from the power plant was less than the projected amount, instead of taking the loss, the company would then transfer the asset to an off-the-books corporation where the loss would go unreported. This type of accounting enabled Enron to write off unprofitable activities without hurting its bottom line.

The mark-to-market practice led to schemes that were designed to hide the losses and make the company appear more profitable than it really was.

To cope with the mounting liabilities, Andrew Fastow, a rising star who was promoted to chief financial officer in 1998, developed a deliberate plan to show that the company was in sound financial shape despite the fact that many of its subsidiaries were losing money.

Fastow and others at Enron orchestrated a scheme to use off-balance-sheet special purpose vehicles (SPVs), also known as special purposes entities (SPEs), to hide its mountains of debt and toxic assets from investors and creditors. The primary aim of these SPVs was to hide accounting realities rather than operating results.

The standard Enron-to-SPV transaction would be the following: Enron would transfer some of its rapidly rising stock to the SPV in exchange for cash or a note. The SPV would subsequently use the stock to hedge an asset listed on Enron's balance sheet. In turn, Enron would guarantee the SPV's value to reduce apparent counterparty risk.

Although their aim was to hide accounting realities, the SPVs were not illegal. But they were different from standard debt securitization in several significant—and potentially disastrous—ways. One major difference was that the SPVs were capitalized entirely with Enron stock.

This directly compromised the ability of the SPVs to hedge if Enron's share prices fell. Just as dangerous as the second significant difference: Enron's failure to disclose conflicts of interest. Enron disclosed the SPVs' existence to the investing public—although it's certainly likely that few people understood them—it failed to adequately disclose the non-arm's-length deals between the company and the SPVs.

Enron believed that their stock price would continue to appreciate—a belief similar to that embodied by Long-Term Capital Management, a large hedge fund, before its collapse in 1998.

Eventually, Enron's stock declined. The values of the SPVs also fell, forcing Enron's guarantees to take effect.

In addition to Andrew Fastow, a major player in the Enron scandal was Enron's accounting firm Arthur Andersen LLP and partner David B. Duncan, who oversaw Enron's accounts. As one of the five largest accounting firms in the United States at the time, Andersen had a reputation for high standards and quality risk management.

However, despite Enron's poor accounting practices, Arthur Andersen offered its stamp of approval, signing off on the corporate reports for years.

By April 2001, many analysts started to question Enron's earnings and the company's transparency.

By the summer of 2001, Enron was in freefall. CEO Kenneth Lay had retired in February, turning over the position to Jeffrey Skilling. In August 2001, Skilling resigned as CEO citing personal reasons. Around the same time, analysts began to downgrade their rating for Enron's stock, and the stock descended to a 52-week low of $39.95. By October 16, the company reported its first quarterly loss and closed its "Raptor" SPV so that it would not have to distribute 58 million shares of stock, which would further reduce earnings. This action caught the attention of the SEC.

A few days later, Enron changed pension plan administrators, essentially forbidding employees from selling their shares for at least 30 days. Shortly after, the SEC announced it was investigating Enron and the SPVs created by Fastow. Fastow was fired from the company that day. Also, the company restated earnings going back to 1997. Enron had losses of $591 million and had $628 million in debt by the end of 2000. The final blow was dealt when Dynegy, a company that had previously announced would merge with Enron, backed out of the deal on November 28. By December 2, 2001, Enron had filed for bankruptcy.

Once Enron's Plan of Reorganization was approved by the U.S. Bankruptcy Court, the new board of directors changed Enron's name to Enron Creditors Recovery Corporation (ECRC). The company's new sole mission was "to reorganize and liquidate certain of the operations and assets of the 'pre-bankruptcy' Enron for the benefit of creditors." The company paid its creditors more than $21.7 billion from 2004 to 2011. Its last payout was in May 2011.

Arthur Andersen was one of the first casualties of Enron's prolific demise. In June 2002, the firm was found guilty of obstructing justice for shredding Enron's financial documents to conceal them from the SEC.

The conviction was overturned later, on appeal; however, the firm was deeply disgraced by the scandal and dwindled into a holding company. A group of former partners bought the name in 2014, creating a firm named Andersen Global.

Several of Enron's executives were charged with conspiracy, insider trading, and securities fraud. Enron's founder and former CEO Kenneth Lay were convicted on six counts of fraud and conspiracy and four counts of bank fraud. Prior to sentencing, he died of a heart attack in Colorado.

Enron's former star CFO Andrew Fastow pled guilty to two counts of wire fraud and securities fraud for facilitating Enron's corrupt business practices. He ultimately cut a deal for cooperating with federal authorities and served more than five years in prison. He was released from prison in 2011.

Ultimately, former Enron CEO Jeffrey Skilling received the harshest sentence of anyone involved in the Enron scandal. In 2006, Skilling was convicted of conspiracy, fraud, and insider trading.

Skilling originally received a 24-year sentence, but in 2013 it was reduced by 10 years. As a part of the new deal, Skilling was required to give $42 million to the victims of the Enron fraud and to cease challenging his conviction. Skilling remains in prison and is scheduled for release on February 21, 2028.