Bank of America Corp.’s controversial purchase of Merrill Lynch & Co. may have cost BofA CEO Ken Lewis his job, but Tom Montag, 52, is doing his best to demonstrate the logic of the deal. Montag’s global markets business booked $6 billion of net income on $17.2 billion of revenue during the first nine months of 2009 — virtually all of the bank’s profits and 18 percent of overall revenue.

Montag, a 22-year veteran of Goldman Sachs Group who had co-headed that firm’s powerful trading unit, largely succeeded in holding Merrill together during a tumultuous period. Now he needs to prove that his bankers and traders can use BofA’s balance sheet to win deals and consistent profits as markets recover.