When Steve Jobs ran Apple (both times), the company saw some of its most innovative moments in engineering and execution.

But it also showed off some of its most important ads and marketing tactics.

One of these campaigns has nearly been forgotten. It took place 37 years ago this month. And if it hadn't happened, it's likely none of the later success would have followed. Here's the story, the ad, and the legacy.

Apple vs. Everyone

Apple went public in 1980 and made 300 millionaires. But just a few months later it faced an existential crisis.

The personal computer market was large and growing, but it was still utterly dwarfed by the market for mainframe business computers, which was dominated by IBM.

And in August 1981, IBM announced it was getting into the personal computer market.

It's funny to think now, but IBM coming into Apple's market then was kind of like Apple or Google or Amazon coming into your market today. Potentially terrifying, maybe even worse.

"Welcome, IBM"

Only, Jobs wasn't really worried. As Walter Isaacson wrote in his 2011 biography, right after IBM announced its new computer, Jobs had his team buy one and tear it apart.

Their consensus was that it sucked ... "a half-assed hackneyed attempt." ... Apple became cocky, not realizing that corporate technology managers might feel more comfortable buying from an established company like IBM rather than one named after a piece of fruit.

Okay, Jobs thought. With "cheeky confidence," as Isaacson put it, he decided to take out a full page ad in The Wall Street Journal, to "cleverly position the upcoming computer battle as a two-way contest between the spunky and rebellious Apple and the establishment Goliath IBM."

Its headline: "Welcome, IBM. Seriously"

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(Added benefit: There were actually other personal computer companies that were just as successful as Apple at the time, like Commodore, Tandy, and Osborne. The Apple ad ignored them.)

The legacy

The ad was a big deal. But Apple didn't win against IBM right away, and there's a reason why people remember the "1984" ad, the "Think Different" campaign, and many others before they remember this one.

It's actually been imitated many times, including in 2015 when a now-bankrupt music streaming company tweeted a similar message to Apple. (Also, the 2016 ad that Slack took out in The New York Times, welcoming Microsoft to its industry.)

But without this "Welcome IBM" ad, would Apple of 1981 have lived long enough to become the Apple of 2018?

Way back when -- ancient history -- it was decisions like these to position Apple as the true rebel, and to frame the battle one-on-one against the entrenched competition, that helped Apple move forward and ultimately have the chance to become the company it is today.

Which is to say, the entrenched competition.