Greenlight Capital President David Einhorn clapped back at recent criticism from Elon Musk on Friday. Einhorn, a well-known Tesla short, also called out the company's shaky record of profitability, contrasting it with his firm's history of positive returns. He also referred to Tesla's "alien dreadnought factory" in a letter published on Twitter. Musk had published a letter earlier Friday addressing Einhorn as "Mr. Unicorn" and accusing the hedge fund of making false statements about Tesla in a recent investor letter. Watch Tesla trade live on Markets Insider.