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

Instagram founder Kevin Systrom and Twitter CEO Jack Dorsey started out as close friends, but had a falling out around the time Instagram sold to Facebook.

According to the book "No Filter: The Inside Story of Instagram" by Sarah Frier, the pair met when they were early employees at Odeo, the audio and video site created by eventual Twitter cofounders Ev Williams and Noah Glass. Dorsey expected to dislike Systrom when he joined as a summer intern in the mid-2000s, but the pair ended up bonding over photography and expensive coffee.

Systrom and Dorsey stayed in touch even after Systrom got a full-time job at Google. Systrom was an early proponent of Twitter (then known as Twttr) and when he started working on Burbn, the precursor to Instagram, he reached out to Dorsey for guidance. Dorsey ended up becoming an early investor, putting in $25,000. When Burbn pivoted to Instagram, Dorsey became one of the app's biggest fans, cross-posting his Instagrams to Twitter and helping the app go viral soon after it launched. Dorsey eventually attempted to buy Instagram, but Systrom declined, saying he wanted to make Instagram too expensive to be acquired, according to Frier.

The Dorsey-Systrom relationship appeared to have soured in 2012, when Dorsey found out that Instagram had signed a deal to be acquired by Facebook, Twitter's biggest rival. According to Frier, Dorsey was hurt that Systrom hadn't called him first to discuss the deal, or to negotiate one with Twitter instead.

Dorsey hasn't posted to his Instagram account since April 9, 2012, when he snapped a photo of an unusually empty San Francisco city bus - according to Frier, it was taken the morning he found out Instagram had sold. While Systrom had been quiet on Twitter for the last few years, he's recently begun using the platform again, and the pair even recently had a pleasant tweet exchange.

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."

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.

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."