On this day in economic and business history...

American Express (AXP 6.22%) joined the Dow Jones Industrial Average (^DJI 0.56%) on Aug. 30, 1982, becoming the first financial component in the index's history. The credit card issuer had only been traded on the New York Stock Exchange for five years, but it was already a leader in financial services, as it had reported $7.2 billion in revenue for the 1971 fiscal year. The addition would prove to be a great long-term advantage for the Dow, as AmEx's shares surged to a 3,600% total gain in the three decades that followed. The company has no doubt benefited from its status as the "premium" card-issuer -- today, AmEx cards account for only about 8% of all cards in circulation, but they ring up nearly a quarter of all purchase volume tallied by the four major card networks.

The little people strike back
Real-estate magnate Leona Helmsley was convicted of tax evasion on Aug. 30, 1989. The conviction brought to a close two years of ethical and legal crusades against the "Queen of Mean," which had started in 1987 when the New York Post published a series of articles alleging that Helmsley and her husband Harry had engaged in a long-standing scheme to claim nearly everything they purchased for their personal use since 1983 as a business expense. The legendarily unpleasant Helmsley would later be sentenced to four years in prison and fined $7.1 million for evading more than a million dollars in taxes.

Helmsley rose to fame in the 1980s as a symbol of the reckless, boundless greed of that decade, and she became immortalized by her own haughty claim that "only the little people pay taxes." At the end of that decadent decade, she was brought low, and even after emerging from prison after 18 months, Helmsley would spend much of the rest of her life tied up in litigation stemming from her blatant disregard of anything beneath her perceived status. However, Helmsley still died a wealthy woman in 2007, with a substantial real-estate portfolio worth many millions of dollars.

Contractors, combine!
Lockheed Corporation and Martin Marietta announced their intent to become Lockheed Martin (LMT 1.71%) in a $10 billion-plus merger on Aug. 30, 1994. The combined company, with $23 billion in revenue, would leapfrog all competitors to become the largest military contractor in the United States.

At the time of the announcement, Lockheed and Martin Marietta employed a combined 170,000 people, but company executives promised to pursue an "aggressive elimination of duplicate costs." Between the two companies, the combined Lockheed Martin had been responsible for building everything from space program rocketry to military transport aircraft -- a veritable smorgasbord of flying stuff for NASA and the Pentagon. Both companies traced their origins to 1912, and each had contributed significantly to the World War II aircraft-building effort, cranking out a combined 15,000 planes.

Lockheed Martin's industry-leading size helped it grow right along with the rest of the military-industrial complex. In the 18 years that followed the completion of its merger, the company doubled its revenue and nearly tripled its net income.

Oil giants, assemble!
ConocoPhillips (COP 1.23%) was created on Aug. 30, 2002, when Conoco and Phillips Petroleum finalized their $16 billion merger. It was the last major oil-producer consolidation of a wave that had produced $285 billion in deals since 1998. The new ConocoPhillips was the sixth-largest public energy company by reserves, the fifth-largest refiner, and the third-largest U.S. energy company, with assets of $75 billion.

ConocoPhillips provided its new (and old) investors with impressive gains over the decade that followed: From the day it completed the merger to the day before Phillips 66 (PSX 0.91%) was spun off as an independent refinery company in 2012, Conoco produced total returns of roughly 300%. Because existing shareholders were granted one share of Phillips 66 for every ConocoPhillips share owned, they can hardly be expected to complain about the divestiture, as the new refiner's stock soared 80% in its first year on the market, compared to a middling 15% gain for the diminished ConocoPhillips.