Erik Pressman in 2370.
Erik Pressman was a Starfleet officer, a rear admiral assigned to Starfleet Intelligence in 2370. At his former rank of captain, he had previously commanded the starship Pegasus in 2358. During its mission to test an illegal interphase cloaking device, his crew mutinied against him when they found out what he was doing, and he escaped with a handful of other survivors, including Will Riker. In 2370, he came aboard the Enterprise to try to retrieve the wreck of the Pegasus, but in reality wanted to retrieve the cloak for further testing. He ordered Riker not to reveal the information about the cloak to anyone else. When the true nature of the mission was revealed, Pressman tried to take command of the Enterprise, but no one would support him. Pressman was eventually placed under arrest for violating the Treaty of Algeron.(TNG: "The Pegasus"; ENT: "These Are the Voyages...")
Background
Pressman was played by Terry O'Quinn.
It is fan speculation that Pressman may have been a member of Section 31. Riker's comment in "These Are the Voyages..." about Pressman's involvement in a "secret" program at Starfleet Security seems to aid that assumption. Also, he says that the cloaking experiment was "for the good of the Federation" and Section 31 states as propaganda that they work for the good of the Federation.