World's largest steelmaker ArcelorMittal has appointed Aditya Mittal as its new Chief Executive Officer (CEO), replacing his billionaire father and the company's founder Lakshmi Mittal, who will become Executive Chairman. The 45-year-old is currently the President and Chief Financial Officer of ArcelorMittal and the CEO of its European business. He joined the company in 1997 from Credit Suisse.