Billionaire Carl Icahn isn't letting up in his quest to get Apple's board to initiate a significant stock buyback. The well-known investor says he's written another letter to CEO Tim Cook, and plans to share its contents on his new website — dubbed Shareholders Square Trade — this Thursday. Icahn alerted his Twitter followers of his plans, later following that up with an appearance on Bloomberg TV, where he continued to press his case. "Apple is not a bank and shareholders did not buy the stock to be a bank," he said during an interview on Street Smart. Icahn insists his quarrel is with Apple's board rather than Cook himself. "I find he is doing a very good job," Icahn said of Apple's CEO. "I know he believes the stock is very cheap, as I do."

Icahn seems dismissive of those who have criticized his buyback proposal. "I think that some of the critics that you listen to are just absurd," he said. "I just heard someone say that Apple might need the money for other things. That is tantamount to saying that Bill Gates should not fix his house because he needs the money for charity." The influential investor says that his latest letter to Cook contains a "pledge" promising that he isn't a short-term investor or looking for a quick flip. "We are not leaving Apple, we are there to stay," Icahn insisted during the interview. Icahn and Cook met for dinner at the end of September, a discussion that Icahn described as "cordial."