As Hugh McColl built North Carolina National Bank into NCNB into Nationsbank into Bank of America, Ken Lewis was the guy who made all those mergers work. McColl was the swashbuckler, Lewis the beancounter. From a 2005 profile in by Fortune by Shawn Tully:

Lewis’s cool restraint impressed McColl. “He always had good credit judgment,” says McColl. “He never fell in love with a company.” But Lewis always liked the consumer business far better than corporate lending–and still does—-for a simple reason: The loan losses in retail tend to be small and predictable, while one big, failed business can blot a balance sheet for years. Lewis’s conservatism about credit is a major reason that, until recently, BofA has focused its expansion on consumer banking. It ain’t sexy, but it pays.

McColl and Lewis could hardly be more different. McColl made deals; Lewis watched the overheads and boosted the sales-per-manager ratio.