The chair of the banking giant Barclays has resigned in the aftermath of an interest-rate fixing scandal that will likely spread to other firms. Marcus Agius announced his departure just days after Barclays was fined $453 million by U.S. and British authorities for manipulating key interest rates. A British probe found Barclays conspired to manipulate the London Interbank Offered Rate, or LIBOR, which provides the basis for rates on trillions of dollars in transactions across the globe. The manipulation meant millions of borrowers paid the wrong amount on their loans. A Justice Department probe of Barclays is continuing, and other banks could be implicated as well.