Two of the world's richest men, Elon Musk and Jeff Bezos, have been sparring for nearly 15 years and the rift seems to be getting wider, with the pair trading barbs in interviews and on social media.
Recently, the Amazon founder tweeted expressing concerns over the Tesla chief's whopping US$44 billion deal to purchase Twitter and how this might give China leverage over the microblogging website.
Bezos's tweet is just the latest in a long-standing feud between the two billionaires. The the main object of their conflict is their respective space ambitions involving Musk's SpaceX and Bezos's Blue Origin.
Here we look back at the reasons why two of the world's most powerful forces don't see eye to eye.
Similar space ambitions in early 2000s
Musk launched SpaceX in 2002 and Bezos launched Blue Origin in 2004; however, both had showed interest in delving into space very early in their careers.
The intent was to use innovation and drastically lower the cost of space travel to send humans further than NASA had gone.
In 1982, Bezos attended the Student Science Training Program at the University of Florida and graduated as a high school valedictorian.
In his graduation speech, Bezos said he dreamed of the day when humans would colonise space.
He told a local newspaper that he intended to get all people off the earth and see it turned into a huge national park.
Thanks to the humungous success of Amazon years later and the subsequent establishment of Blue Origin, Bezos is still clinging to his dream.
Around the same time as Bezos was working on establishing his dream project, Musk was already a millionaire from the sale of Zip2 to Compaq for roughly US$300 million.
He was also involved with the nonprofit Mars Society since 2001 and took inspiration from plans to place a growth chamber for plants on Mars. He was so impressed with the idea, he considered funding the project himself.
After facing rejection by Russian companies to buy refurbished intercontinental ballistic missiles (ICBMs) that could send the greenhouse payloads into space, Musk decided to start his own company that could build affordable rockets.
The sale of PayPal to eBay earned him roughly US$165 million, which he parlayed to establish Space Exploration Technologies Corp., traded as SpaceX, in May 2002.
An unfriendly dinner discussion in 2004
According to a report in Business Insider, Bezos and Musk met in 2004 to discuss their respective reusable-rocket ambitions at a time when both their companies were relatively new.
The discussion, however, didn't turn out to be fruitful with resistance to ideas from both ends leading to subtle rivalry between the two.
In Christian Davenport's book, The Space Barons, Musk reveals what exactly transpired during that discussion.
"I actually did my best to give good advice, which he largely ignored," Musk said after the meeting.
Following this dinner, the two billionaires stayed out of each other's hair for almost a decade.
Conflict over leasing a NASA launchpad in 2013
SpaceX tried to get exclusive use of a NASA launchpad in 2013 but this was opposed by rivals Blue Origin and United Launch Alliance.The two companies filed a formal complaint to prevent SpaceX from using the pad, but SpaceX eventually won the right to take over the pad.
During the course of this protest, Bezos had proposed converting the launchpad into a commercial spaceport available to all launch companies but Musk lashed out, calling the proposal a "phony blocking tactic".
He came down heavily on Blue Origin, saying: "Despite spending 10 years in development, it had not yet succeeded in creating a reliable suborbital spacecraft."
Musk aggravated the friction by claiming SpaceX would gladly accommodate needs of their rivals, "if they managed to show up in the next five years with a vehicle qualified to NASA's human rating standards that can dock with the Space Station", as reported by Space News in 2013.
Patent battle in 2014
When Blue Origin was granted a patent for drone ships in 2014, SpaceX petitioned to invalidate it and won on the argument that drone ships had been around for decades and could not be patented.
Drone ships are used to land rocket boosters. Blue Origin's ownership of the patent would lead to SpaceX paying to use the technology.
Blue Origin was forced to withdraw its claims to the patent after the court supported SpaceX.
Twitter wars and taking potshots at each other in interviews
In 2015, when Blue Origin successfully landed its New Shepard rocket, Bezos tweeted a video calling it: "The rarest of beasts — a used rocket."
The rarest of beasts - a used rocket. Controlled landing not easy, but done right, can look easy. Check out video: https://t.co/9OypFoxZk3
— Jeff Bezos (@JeffBezos) November 24, 2015
But Musk quipped that SpaceX had performed the feat three years earlier.
— Elon Musk (@elonmusk) November 24, 2015
When SpaceX landed its Falcon 9 spacecraft, Bezos took a different approach and wished them luck, to which Musk responded with a 'thank you' and a 'flying kiss' emoticon, perhaps suggesting some light hearted humour and healthy competition.
— Jeff Bezos (@JeffBezos) February 5, 2018
— Elon Musk (@elonmusk) February 5, 2018
When Amazon announced its plan to launch internet-beaming satellites in 2019, and again when it acquired self-driving-taxi company Zoox, Musk promptly tweeted that Bezos was a 'copy cat'.
After Blue Origin revealed its concept for a lunar-landing vehicle called Blue Moon, Musk posted a tweet and said: "Putting the word 'Blue' on a ball is questionable branding."
In an interview with Financial Times in 2021, Musk said Bezos took himself too seriously.
While Bezos has been less direct with his tweets against Musk, in 2019, during a chat, he belittled the idea of reaching Mars and called it "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 challenged.
Most recently, in May 2022, Bezos also tweeted concerns over how Musk's takeover of Twitter might give China advantage over the platform.
Interesting question. Did the Chinese government just gain a bit of leverage over the town square? https://t.co/jTiEnabP6T
— Jeff Bezos (@JeffBezos) April 25, 2022
Dispute over talent poaching
Musk has not only accused Amazon of monopoly in publishing - following Amazon's refusal to publish a book about the coronavirus by writer Alex Berenson - but he has also accused the Blue Origin founder of stealing talent from SpaceX.
"Blue Origin does these surgical strikes on specialised talent, offering like double their salaries," Musk told his biographer, Ashlee Vance.
But Musk's most spontaneous dig was when the BBC asked him about Bezos in 2016, and he responded by asking, "Jeff who?".