What is the name of the FBI agent who works on the Soprano case?

The FBI agent who works on the Soprano case is Dwight Harris. Played by Matt Servitto, Harris is a supervisory FBI agent assigned to investigate the DiMeo crime family through the Newark Organized Crime Division Task Force.

Harris is more than a conventional law-enforcement antagonist. After the September 11 attacks, he is reassigned to the Joint Terrorism Task Force in Pakistan. He later approaches Christopher Moltisanti and Tony Soprano for information about possible terrorism-related activity involving people connected to the New York and New Jersey port network.

Tony and Harris develop a transactional relationship. Tony provides information about Ahmed and Muhammad, two men associated with Christopher's stolen-credit-card operation, while Harris offers goodwill that could potentially help Tony in a future RICO case. Harris also passes along information about threats from Phil Leotardo's Lupertazzi organization.

In the series finale, “Made in America,” Harris tells Tony that Phil has been using pay phones in Oyster Bay. After Phil is killed, Harris reacts with the memorable line, “We're gonna win this thing!” His role shows how the FBI investigation becomes entangled with the same alliances and information trades that shape the mob's world.