When Weill left American Express in 1985, Dimon followed . The pair ran Commercial Credit, a company they would build into the financial-services conglomerate Citigroup .Dimon's finance skills were clear from early on. At the behest of his mentor, the financier Sandy Weill , he turned down offers from Goldman Sachs and Morgan Stanley to accept a job at American Express after graduating from Harvard.Dimon graduated from Tufts University, where he majored in psychology and economics. After a stint as a manage ...