Musk and Bezos are two of the most powerful CEOs in the world. Bezos is currently the wealthiest living person and runs Amazon’s sprawling empire while also involving himself in Blue Origin’s quest to send people to the moon. Musk is a dual CEO, manning the ship at both Tesla and SpaceX. Over the years, their not-so-subtle rivalry has even given way to Twitter spats and name-calling.

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Here’s how the rivalry began and everything that’s happened since.

Back in the early 2000s, Jeff Bezos wasn’t yet the titan he is today

Bezos founded Amazon in 1994 and the company went public in 1997. But Amazon wasn’t yet the powerhouse it would become – it was years before the company would launch Prime, start its own streaming service, or create its cloud infrastructure service, Amazon Web Services.

But Bezos had always been interested in space. He told The Miami Herald in 1982, after he graduated high school as valedictorian, that he wanted to create outer space colonies for millions of people.

As a result of that long-held interest in leaving Earth, Bezos launched Blue Origin in 2000, a new start-up focused on human space flight.

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Elon Musk was already a millionaire several times over, but he hadn’t become CEO of Tesla yet

Around the time Bezos was launching Blue Origin, Musk had already sold Zip2, a start-up he launched with his brother, Kimbal, to Compaq for roughly US$300 million. Musk was in the process of building PayPal, which would later be sold to eBay for US$1.5 billion.

Musk made about US$160 million off the PayPal sale and used that money to launch SpaceX in 2002.

“In the beginning, I actually wouldn’t even let my friends invest because everyone would lose their money,” Musk said during an interview at South by Southwest in 2018. “I thought I’d rather lose my own money.”

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The Musk-Bezos rivalry appears to date back to 2004 when the two CEOs met for dinner

By 2004, both Blue Origin and SpaceX were still in their infancy – neither company had completed any launches yet.

But that didn’t stop a rivalry from heating up: when the two met to discuss their respective reusable rocket ambitions it apparently did not go well.

“I actually did my best to give good advice, which he largely ignored,” Musk said after the meeting, according to Christian Davenport’s book, The Space Barons.

From 2004 onwards, Musk and Bezos appeared to keep to themselves. But their rivalry continued in 2013 when things became contentious over leasing a Nasa launch pad

In 2013, SpaceX tried to get exclusive use of a Nasa launch pad. Blue Origin (along with SpaceX rival United Launch Alliance) filed a formal protest with the government to prevent SpaceX from using the pad – Bezos proposed converting it “into a commercial spaceport available to all launch companies.”

Musk called the move a “phoney blocking tactic” and took another swipe at Blue Origin.

"[Blue Origin] has not yet succeeded in creating a reliable suborbital spacecraft, despite spending over 10 years in development,” Musk told Space News at the time. “If they do somehow show up in the next five years with a vehicle qualified to Nasa’s human rating standards that can dock with the Space Station, which is what Pad 39A is meant to do, we will gladly accommodate their needs.”

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“Frankly, I think we are more likely to discover unicorns dancing in the flame duct,” he added.

SpaceX eventually won the right to take over the pad.

In 2014, the two companies got into a patent battle when Blue Origin was granted a patent for drone ships, which are used for landing rocket boosters. SpaceX petitioned to invalidate the patent

Blue Origin’s ownership of the patent would mean SpaceX would need to pay to use the technology. SpaceX argued that the science in the patent was “old hat,” given that the concept of drone ships has been around for decades.

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A judge sided with SpaceX, leading to Blue Origin withdrawing most of the claims in the patent.

In recent years, Musk and Bezos have been more public about their feud, taking their rivalry to Twitter

Both execs have seized on opportunities to take shots at the other, most often sniping at each other over reusable rockets. After Blue Origin successfully landed its New Shepard rocket in 2015, Bezos tweeted a video calling it “the rarest of beasts – a used rocket”.

Musk responded, saying SpaceX had performed the feat three years prior.

When SpaceX landed its Falcon 9 spacecraft, Bezos took the opportunity to needle Musk on Twitter.

The feud isn’t just about space ambitions, however. Musk has taken issue with Blue Origin’s hiring practices and has taunted Bezos in interviews

Musk told his biographer, Ashlee Vance, that Blue Origin has repeatedly tried to snag talent away from SpaceX. “Blue Origin does these surgical strikes on specialised talent offering like double their salaries,” Musk said in Vance’s 2015 biography. “I think it’s unnecessary and a bit rude.”

Musk also revealed that SpaceX set up an email filter for the words “blue” and “origin,” according to Space News.

When the BBC asked Musk about Bezos in 2016, he responded, “Jeff who?”

Musk is known for being outspoken on Twitter and that has included jabs at Bezos

Musk has repeatedly and publicly called Bezos a “copycat” – once after Amazon announced its plan to launch internet-beaming satellites and again when Amazon acquired self-driving-taxi company Zoox.

Musk poked at Bezos in 2019 after the unveiling of Blue Origin’s concept for a lunar-landing vehicle, called Blue Moon.

“Putting the word Blue on a ball is questionable branding,” he tweeted.

Musk later mocked up a screenshot of The New York Times’ article that changed the name from “Blue Moon” to “Blue Balls”.

“Oh stop teasing, Jeff,” Musk wrote.

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For his part, Bezos has been less overt about his distaste for Musk and SpaceX, but he’s made veiled comments about his thoughts on the company’s plans

While Bezos has stopped short of calling out Musk directly, he has taken aim at Musk’s biggest ambition: colonising Mars, the main goal of SpaceX.

Bezos’ focus is on getting humans to the moon and he’s described the idea of reaching Mars as “un-motivating”.

“Go live on the top of Mount Everest for a year first and see if you like it, because it’s a garden paradise compared to Mars,” Bezos said in 2019.

During his presentation for Blue Moon, Bezos referenced SpaceX’s Mars ambitions once again, titling a slide about Mars “FAR, FAR AWAY”.

In July, Musk appeared to make yet another dig at Bezos – this time about his age – in an interview with The New York Times

In a wide-ranging Times interview, Musk, 49, took the opportunity to comment on Blue Origin, appearing to imply that Jeff Bezos, 56, is too old and Blue Origin too slow to ever make real progress.

“The rate of progress is too slow and the amount of years he has left is not enough, but I’m still glad he’s doing what he’s doing with Blue Origin,” Musk said.

Though the pair’s main point of contention appears to be space, Musk has made other pointed remarks about Amazon, recently calling the company a monopoly

After Amazon’s publishing service refused to publish a book about the coronavirus by writer Alex Berenson, Musk tweeted at Bezos that the situation was “insane” and called for Amazon to be broken up.

Musk’s comments were in response to Amazon’s Kindle Direct Publishing service refusing to publish Berenson’s book titled Unreported Truths about Covid-19 and Lockdowns. Berenson tweeted a screenshot of an email he says he received from Amazon and said the company “censored” his book. The screenshot appeared to show the publishing division saying the book does not comply with its guidelines.

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Amazon later told Business Insider the book was removed in error and would be reinstated.

But both Bezos and Musk have continued to make progress – and grow their wealth – even as their rivalry continues on

In May, SpaceX experienced a historic first: the company successfully launched two Nasa astronauts into space.

“This is a dream come true for me and everyone else at SpaceX,” Musk said at the time. “I didn’t even dream that this would come true.”

Bezos remains the richest person in the world. On one day earlier in July, Bezos added US$13 billion to his net worth, nudging his wealth to more than US$189 billion.

While Bezos is facing government scrutiny over Amazon’s potentially anticompetitive behaviour, Amazon continues to thrive – the company reported a huge beat for its second-quarter earnings after a surge in demand during the coronavirus crisis.

Regardless of where their rivalry stands, the two moguls won’t stop being competitors any time soon: these days, their companies are both submitting designs for lunar landers to Nasa for a mission to return humans to the moon by 2024.

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This story originally appeared in Business Insider.