Jeff Bezos and Elon Musk have feuded for over a decade about space travel. Here are 9 rivalries between some of the world's biggest tech CEOs.

Oracle founder Larry Ellison and Salesforce CEO Marc Benioff met when Benioff began working at Oracle when he was 23. He was a star early on, earning a "rookie of the year" award that same year and becoming Oracle's youngest VP by age 26. He spent 13 years at Oracle, during which he became a trusted lieutenant to Ellison.

Benioff began working on Salesforce with Ellison's blessing, and Ellison became an investor, putting in $2 million early on.

But since then, the duo has publicly feuded on multiple occasions. In 2000, Oracle launched software that directly competed with Salesforce. Benioff asked Ellison to resign from Salesforce's board, and Ellison refused (he eventually left the board, but Benioff let him keep his stock and options).

Over the years, Benioff and Ellison have sparred off and on: Ellison once mocked Salesforce, calling it an "itty bitty application" that's dependent on Oracle, while Benioff has called Oracle a "false cloud." And in 2011, Ellison ordered that Benioff be removed from the speaker lineup of Oracle's OpenWorld conference, which Benioff said was because Oracle was afraid he'd give a better speech.

But throughout it all, Benioff has described Ellison as his mentor. "There is no one I've learned more from than Larry Ellison," Benioff said in 2013.

There is no love lost between Apple CEO Tim Cook and Facebook CEO Mark Zuckerberg.

The two moguls have traded insults over the years, beginning as early as 2014, when Cook said in an interview that "when an online service is free, you're not the customer. You're the product."

Shortly after, Zuckerberg appeared noticeably tense in an interview with Time when the subject of Cook's comments came up, saying, "'What, you think because you're paying Apple that you're somehow in alignment with them? If you were in alignment with them, then they'd make their products a lot cheaper!'"

But the tension between Cook and Zuckerberg came to a head in the aftermath of Facebook's Cambridge Analytica scandal, in which private Facebook user data was stolen from 50 million users. In 2018, Recode's Kara Swisher asked Cook what he would do if he was in Zuckerberg's shoes, to which he responded: "What would I do? I wouldn't be in this situation."

Zuckerberg was reportedly so incensed by Cook's comments that he asked executives to switch to Android phones.

In a company blog post in 2018, Facebook confirmed the feud between the two execs: "Tim Cook has consistently criticized our business model and Mark has been equally clear he disagrees."

In the early days of Apple and Microsoft, Steve Jobs and Bill Gates got along — Microsoft made software for the Apple II computer, and Gates was a frequent guest in Cupertino, where Apple is headquartered.

But the tides started to turn in the early '80s, when Jobs flew up to Microsoft's headquarters in Washington to try to convince Gates to make software for the Macintosh computer. Gates later described it as "a weird seduction visit" and said he felt like Jobs was saying "I don't need you, but I might let you be involved."

Still, they remained relatively friendly until 1985, when Microsoft launched the first version of Windows and Jobs accused him of ripping off the Macintosh.

"They just ripped us off completely, because Gates has no shame," Jobs later told his biographer, Walter Isaacson, to which Gates replied: "If he believes that, he really has entered into one of his own reality distortion fields."

The duo traded barbs for years, with Jobs calling Gates boring and Gates calling Jobs "weirdly flawed as a human being." Tensions remained high even after Microsoft invested in Apple to keep it afloat, with both Gates and Jobs insulting each other and their companies' products time and time again.

Still, they clearly respected and admired each other, despite their animosity. When Jobs died in 2011, Gates said: "I respect Steve, we got to work together. We spurred each other on, even as competitors. None of [what he said] bothers me at all."

Amazon CEO Jeff Bezos and SpaceX and Tesla CEO Elon Musk aren't competitors in any earthly pursuits, but they're bitter rivals when it comes to outer space.

Bezos founded his rocket company, Blue Origin, in 2000, while Musk founded SpaceX in 2002. Two years later, the pair met for dinner, and even then, things were getting testy.

"I actually did my best to give good advice, which he largely ignored," Musk said after the meeting.

In 2013, their rivalry heated up when SpaceX tried to get exclusive use of a NASA launch pad and Blue Origin (along with SpaceX rival United Launch Alliance) filed a formal protest with the government. Musk called it a "phony blocking tactic" and SpaceX eventually won the right to take over the pad. Months later, the two companies got into a patent battle, and soon after, Bezos and Musk took their feud public, trading barbs on Twitter.

Once, when the BBC asked Musk about Bezos, he responded, "Jeff who?" For his part, Bezos has frequently criticized the idea of colonizing Mars — a main goal of SpaceX — describing the idea as "un-motivating."

As recently as May 2019, Musk jabbed at Bezos again, calling him a copycat for Amazon's plan to launch internet-beaming satellites.

Twitter CEO Jack Dorsey and Zuckerberg have never seemed particularly chummy, but the rivalry between the two execs seems to have grown worse in the last few years.

Facebook has come under fire during the last several months over its decision not to fact-check political ads. In response, Dorsey announced last October that Twitter was suspending political advertising altogether, saying "political message reach should be earned, not bought."

Dorsey also said at an event that month that Zuckerberg's argument that Facebook is an advocate for free speech "a major gap and flaw in the substance he was getting across," and that "there's some amount of revisionist history in all his storytelling."

For his part, Zuckerberg hasn't been shy about criticizing Twitter, saying in an all hands that "Twitter can't do as good of a job as we can," according to leaked audio obtained by The Verge.

In December, Dorsey unfollowed Zuckerberg on Twitter.

Gates and Ellison may have patched things up these days, but back in the late '90s and early 2000s, they were enemies.

While it seems like there's no real bad blood currently between the two, there definitely appears to have been a touchy relationship between the them throughout the '90s, mostly defined by Ellison trying to outdo Gates.

"He's utterly obsessed with trying to beat Bill Gates," former Microsoft CTO Nathan Myhrvold once told Vanity Fair. "I mean, the guy's got six billion bucks. You'd think he wouldn't be so dramatically obsessed that one guy in the Northwest is more successful. [With Larry] it's just a mania."

Their animosity partly stemmed from Ellison's close friendship with Steve Jobs, a frequent opponent of Gates. But things took a more serious turn in 2000 when Microsoft was being investigated by the federal government over antitrust violations. At the time, several groups were openly supportive of Microsoft, and Ellison suspected they were being funded by Microsoft itself. He hired private investigators to in an attempt to out Microsoft and help out the feds.

Eventually, Microsoft lost the suit, and Gates stepped down as Microsoft CEO.

Snap CEO Evan Spiegel and Mark Zuckerberg seemed to get off on the wrong foot right from the start, beginning with what may have been a Spiegel brush-off in 2012.

Snap had reportedly turned down an acquisition offer from Facebook on three separate occasions.

Spiegel and Zuckerberg haven't been friendly since. Facebook has mimicked many of Snapchat's features over the years — both on its own app and its subsidiary, Instagram — and the CEOs have made jabs at each other in public. In 2018, after Facebook cloned yet another Snapchat feature, Stories, Spiegel said: "We would really appreciate it if they copied our data protection practices also," a dig at Facebook's various privacy scandals.

In 1997, Dell founder and CEO Michael Dell was asked for his opinion on Apple, which, at the time, was in dire straits. He responded that he'd "shut it down and give the money back to the shareholders."

That comment irritated Steve Jobs, who told his team in response: "The world doesn't need another Dell or HP. It doesn't need another manufacturer of plain, beige, boring PCs. If that's all we're going to do, then we should really pack up now." At an Apple keynote shortly after, Jobs said Dell's comments were "rude" and told him that Apple was coming for him.

Dell later softened his comments, saying that he was trying to make clear that he wasn't for hire.

But Dell rankled Jobs enough that, in January 2006, Jobs sent around this memo to the entire company: "Team, it turned out that Michael Dell wasn't perfect at predicting the future. Based on today's stock market close, Apple is worth more than Dell. Stocks go up and down, and things may be different tomorrow, but I thought it was worth a moment of reflection today."

Mark Zuckerberg and Instagram founder Kevin Systrom used to get along well — so well that Zuckerberg bought Instagram for $1 billion in 2012.

But in the intervening years, the relationship between the two executives seemingly fell apart. When asked why he left, Systrom said, "no one ever leaves a job because everything's awesome."

According to an April 2019 piece from Wired's Nick Thompson and Fred Vogelstein, Systrom and cofounder Mike Krieger left because of increasing tensions with Zuckerberg. Zuckerberg reportedly became increasingly controlling, banning Systrom from doing magazine profiles without approval, taking away Facebook tools that helped Instagram grow, testing location-tracking while Systrom was out on paternity leave, and adding a new button to Instagram that Systrom detested.