Robert McCann, head of Merrill Lynch’s “thundering herd” of 16,000 financial advisers, is leaving the firm that he has worked for, with one interruption, since 1982.

His departure, described by a Merrill Lynch source as voluntary, was disclosed late Monday in a company-wide announcement by John Thain, who was chief executive of Merrill, but following the firm’s acquisition by Bank of America last week, is now president of global banking, securities and wealth management at BofA.