Behind a set of imposing metal doors in an easy-to-miss office building in a New York City suburb, a small team manages billions of dollars for a Russian oligarch.For years, a group of wealthy Russians have used Concord Management LLC, a financial-advisory company in Tarrytown, N.Y., to secretly invest money in large U.S. hedge funds and private equity firms, according to people familiar with the matter.A web of offshore shell companies makes it hard to know for sure whose money Concord manages. But several of the people said the bulk of the funds belong to Roman Abramovich, a close ally of President Vladimir V. Putin of Russia.Concord is part of a constellation of American and European advisers — including s …
