A paper stock certificate.

Image source: Getty Images.

When it comes to the world's most famous stock market indexes, nothing tops the Dow Jones Industrial Average (DJINDICES:^DJI). Created by Charles Dow in 1896, the Dow is the second-oldest stock market index after the Dow Jones Transportation Index, which Charles Dow also created.

When it was originally formed, the Dow was composed of just 12 companies, including American Tobacco, Chicago Gas, U.S. Rubber, and American Cotton Oil. Today, the Dow includes 30 multinational companies that range from tech giant Apple, the largest publicly traded company in the world with a market cap of more than $800 billion, to property and casualty insurer Travelers Companies, which is minute by comparison with a $35 billion market cap.

Throughout the Dow's history, it has changed its component stocks more than 50 times, basing those changes partly on innovation and the shifting American economy. Today, we'll take a closer look at which six current Dow components have managed to hang around the longest. 

A General Electric gas turbine being hoisted by cables.

Image source: General Electric.

1. General Electric

As far as Dow components go, General Electric (NYSE:GE) is a veritable relic. It's the only company that has been in the Dow since the index was formed in 1896. GE was briefly bounced from the Dow for seven months between September 1898 and April 1899, and for three months between April 1901 and July 1901, but it has otherwise been a foundation of the Dow for the past 121 years. 

General Electric's diversified business model has been a key to its long-term success. A recent divestiture of its financial arm, which is now known as Synchrony Financial, should allow the company to return to its roots and focus on industrial equipment. Manufacturing everything from wind turbines to MRI machines for hospitals, GE's diverse operating portfolio has been a reliable source of long-term profitability.

An offshore oil drilling platform.

Image source: Getty Images.

2. ExxonMobil

Integrated oil and gas giant ExxonMobil (NYSE:XOM) has been a member of the Dow since Oct. 1, 1928, which is when the index was expanded from 20 components to 30 components. However, in the records of this historical event, Exxon's name is nowhere to be found: Back in 1928, the company was known as Standard Oil Co. of New Jersey. The company wasn't unveiled to the world as "Exxon" until 1972, and it didn't become ExxonMobil until its megamerger with Mobil in 1999. 

Being one of the largest oil and gas companies on Earth certainly has its perks. ExxonMobil has been able to use its vertically integrated operations to hedge against considerably lower crude prices since 2014; while falling oil prices hurt the exploration and production business, they benefit the refining business. Exxon also recently uncovered a huge oil field off Guyana's coast that could contain up to 2 billion barrels in reserves. ExxonMobil's future looks bright, and its spot in the Dow seems secure for now.

An assortment of P&G consumer brands, including Tide, Crest, and Charmin.

Image source: Procter & Gamble.

3. Procter & Gamble

Perhaps known best for Tide detergent, Crest toothpaste, and its dozens of other consumer products, Procter & Gamble (NYSE:PG) wound up being added to the Dow on May 26, 1932, and it's been there ever since. The never-ending demand for P&G's products has a lot to do with its longtime Dow membership -- and its success. Since the beginning of 1970, Procter & Gamble's stock is up nearly 3,000%, and if you include the dividends it has paid out, that return spikes to 6,600%.

P&G's secret sauce is a combination of steady consumer demand and great marketing. Procter & Gamble sells many products that, like the aforementioned detergent and toothpaste, are purchased regardless of whether the economy is booming or in recession. This gives P&G reliable pricing power. The icing on the cake is that few, if any, companies spend more on advertising each year than P&G, which keeps its products at the front of consumers' minds. 

A farmer using a tractor to spray his crop with an insect repellent.

DuPont's chemicals help protect farmers' crops in order to maximize their yield. Image source: Getty Images.

4. DuPont

Chemicals giant DuPont (NYSE:DD) is fourth in line in terms of seniority: In 1935, DuPont, along with National Steel, replaced Borden and Coca-Cola on the Dow Jones Industrial Average. This coming November will mark the company's 82nd consecutive year on the index, though the company also spent 18 months on the Dow back in the mid-1920s.

Chemical companies like DuPont are cyclical in nature, so they rely on the U.S. economy to expand in order to grow their business. Thankfully, even though recessions are a normal part of the economic cycle, expansionary periods tend to last much longer than recessions, which has fueled DuPont's growth. Its future is looking even brighter now that U.S. antitrust regulators have given the company the green light to merge with rival Dow Chemical (no relation to the index we've been discussing). 

A person using their finger to test an in-home smoke alarm.

Image source: United Technologies.

5. United Technologies

United Technologies (NYSE:RTX), which is involved in everything from elevators to climate control and aerospace systems for aircraft, did a couple of brief stints on the Dow in the early 1930s, but it wasn't until 1939 that it gained a solid position on the index. United Technologies, then known as United Aircraft and Transport Corporation, has been a Dow fixture ever since.

Like some of its more senior Dow components, United Technologies is a cyclical company that relies on a growing U.S. economy to increase demand for its products and services. The company's diversification is what's really been its foundation all these years. Its main business units -- Otis Elevator, Pratt & Whitney aircraft engines, UTC Aerospace Systems, and UTC Climate, Controls & Security -- each produce roughly 20% to 30% of its annual sales. 

A woman sticking Post-It notes on her wall.

Image source: Getty Images.

6. 3M

There's a sizable gap in "seniority" between fifth-place United Technologies and sixth-place 3M (NYSE:MMM), which has been a Dow component since Aug. 9, 1976. 3M is best-known for its Post-It notes and Scotch Tape, though it also makes laminates, protective equipment, medical and dental products, and car-care products, to name a few things. When it joined the Dow, it was called Minnesota Mining and Manufacturing -- thank goodness for the name change to 3M in 2002!

For the time being, 3M's four-decade tenure within the Dow looks safe, given its diversified product portfolio. Of course, investors in 3M are also accustomed to the cyclicality associated a company that relies on consumers to drive results. But with 3M's stock up 2,700% since it joined the Dow 41 years ago (6,400% including dividends), few of its long-term investors are liable to complain.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.