The letter comes two days after Musk tweeted an unfounded and disparaging claim about Vernon Unsworth, an expert caver who participated in the rescue mission that saved 12 boys and their soccer coach who spent almost three weeks trapped in a flooded cave in Thailand.
British cave rescuer Vern Unsworth was attacked on Twitter by Elon Musk, including being called "pedo guy" in a since-deleted tweet, after Unsworth criticized Musk's plan to save children stuck in an underwater cave in Thailand using a miniature submarine.
Mr Unsworth had earlier said the mini-sub built by Mr Musk's team, and flown to Thailand before being rejected as inappropriate for the rescue mission by Thai officials, would have had "absolutely no chance of working".More news: Trump, Putin begin day of meetings in Helsinki
What's weird about Musk's tweet is that it came on July 15, a full five days after the boys were rescued.
Makers of all-electric cars and their buyers qualify for the $7,500 subsidy until the company sells a cumulative 200,000 vehicles in the United States.
"I have a lot of support from people around the world astonished by his unfounded comments", he said.
On Sunday, Musk unleashed on Unsworth, writing on Twitter that he meant to build the child-size submarine he offered to rescuers for the Thailand mission that they rejected.
He doubled down on the claim, tweeting to more than 22 million followers: "Bet ya a signed dollar it's true".More news: Obama in ancestral home Kenya to launch sister's project
Mr O'Donnell said Mr Musk has fallen into a "hero worship persona" but has failed to live up to the responsibility that implies. "I believe he has called me a paedophile". "I am not gonna make any further comment about him but I think people realize what sort of a guy he is". "And so essentially if you attack me, it is therefore OK for me to attack back", Musk told Bloomberg.
Musk has for years said he is proudly, aggressively unfocused - a billionaire known for his visionary ventures in electric cars, underground supertrains, artificial intelligence and space travel.
Mr Patrick Moorhead, analyst and consultant with Moor Insights & Strategy, said there were "some similarities up to this point" between Mr Musk and Mr Jobs, but that the latest personal insult appeared to cross a line. When documents revealed he donated to a Republican political group, despite his criticism of the current administration, he responded by saying he gives "to both parties to maintain dialogue".More news: Federation Internationale de Football Association confirm winter World Cup dates for Qatar 2022