Elon Musk is offering to buy Twitter for $43 billion in cash  Last week, Elon Musk became Twitter's largest shareholder. The Tesla and SpaceX CEO was going to join Twitter's board — then he wasn't 

Now the world's richest person is offering to buy the company for $43 billion — $54.20 per share — in cash, according to a regulatory filing posted Wednesday. 

Elon Musk has made an offer to buy Twitter (TWTR) and take it private, saying he believes the company needs to be "transformed. 

According to an SEC filing, Musk has offered to acquire all the shares in Twitter he does not own for $54.20 per share, valuing the company at $41.4 billion. 

That represents a 38% premium over the closing price on April 1, the last trading day before Musk disclosed that he had become Twitter's biggest shareholder, 

and an 18% premium over its closing price Wednesday. Musk said the cash offer was his "best and final offer," according to the SEC filing,

Musk says he believes in the potential of Twitter and that the social media company needs to be transformed. 

My offer is my best and final offer and if it is not accepted, I would need to reconsider my position as a shareholder, 

Musk said in the filing. (He holds more than 9% of Twitter's shares.) "Twitter has extraordinary potential. I will unlock it," Musk added.