A Starfleet admiral who orders Captain Picard in 2370 to take Admiral Erik Pressman aboard and give him full co-operation on a secret mission.
Admiral Margaret Blackwell is a Starfleet flag officer. She appears in the episode The Pegasus, played by Nancy Vawter.
She contacts the Enterprise-D with priority orders. The ship is to meet Pressman, of Starfleet Intelligence, and go to the Devolin system, where wreckage of the USS Pegasus may have been found. Blackwell tells Picard that Pressman will direct the mission and that the Romulans must not reach the ship first.
She explains very little, and Picard is left to work out for himself what was aboard the Pegasus and why Commander Riker, who served on it as an ensign, has become so guarded. The answer is an illegal cloaking device built in breach of the Treaty of Algeron. How much Blackwell knew is not made clear.