A private investment firm, Black Rock, has agreed to put up $875 million to buy a stake in the Authentic Sports Group (ABG), according to the Wall Street Journal, valuing the company at around $4 billion. It will apparently replace Leonard Green Partners as the largest shareholder in the American group, founded by Jamie Salter ten years ago. ABG owns several important sports brands including Airwalk, Prince, Spyder, Vision and Volcom, in addition to the licensing rights for celebrities such as Marilyn Monroe, Muhammad Ali and Elvis Presley.