In the mid-2370s, Admiral Bullock was the role played by a member of Species 8472 in the training simulation on the Terrasphere 8, designed to accurately simulate Earth. "Bullock" was a high-ranking member of Species 8472 who reported directly to "Boothby."
Later, after Species 8472 confirmed that they'd been discovered, "Bullock" reported to Boothby that Voyager was approaching, and charged the biosphere's weapons. When the two tried searching for a diplomatic answer, he was sent, along with Boothby and Valerie Archer. His stance was firmly that the Federation couldn't be trusted, even after Boothby had been convinced. After a truce was reached, he had his assistant, Kinis, give Neelix a tour, while he personally showed Tuvok around before Voyager left. (VOY: "In the Flesh")
Background information Edit
Admiral Bullock was played by Tucker Smallwood.
It is unclear if there was a real Starfleet Admiral Bullock or if the persona was created by Species 8472. According to Boothby and Kathryn Janeway, the simulation was incredibly accurate of Starfleet Headquarters and its personnel. The Star Trek Encyclopedia (4th ed., vol. 1, p. 109) described the persona created by Species 8472 as a re-creation of Admiral Bullock.
In Star Trek Conquest game, Bullock was a player character in a reality where the Milky Way Galaxy was embroiled in conflicts between multiple species and cultures. In 2364, Bullock held the rank of commodore and was in command of a fleet during the conflict. Bullock had an opportunity to be promoted all the way to fleet admiral based on his battle experiences, but at the cost of constant vigilance against the possibility of combat with Klingons, Romulans, Breen, Cardassians, and Jem'Hadar forces, as well as in danger from the Xindi, Ferengi, Orions, and Borg that had taken over the systems that had become neutral as they fell away from the Klingon Empire, Romulan Star Empire, Breen Confederacy, Cardassian Union, and Dominion governments.
According to the novel The Needs of the Many the real Admiral Bullock has the first name Gareth.