As a captain of a raider vessel, Dreen and his crew had been harassing Federation shipping when they were intercepted by the USS Enterprise, under the command of Captain Christopher Pike. Pike hailed Dreen, and managed to convince Dreen that he was not the ideal Starfleet officer, that instead he was looking to leave the fleet, and engage in a more profitable career. Pike then sent Spock with a "gift" of dilithium over to Dreen's ship. When the shields on Dreen's ship were dropped for transport, in addition to Spock, Pike also had his transporter chief beam a security team over to the Merkaan ship, which seized control of the vessel.
After Dreen's stolen cargo was confiscated, Dreen was released, and returned home in disgrace. The shame of Pike outwitting him was such that several years later doctors were forced to replace his stomach with an artificial organ. Dreen worked hard to earn another command in the Merkaan fleet, while planning revenge against Pike and Spock.
In 2268, Dreen was sent to capture a Federation colony with a force of three Merkaan ships. Initially, the raid was successful, and once again it was the Enterprise who confronted the Merkaans. Spock learned a former Enterprise crew member was working as a colony administrator, and came up with the coded phrase "Boyce's birthday." This was in reference to a birthday party held on the Enterprise for Doctor Phillip Boyce, during which some chemicals were spilled on to another substance, and the resulting gas knocked out several crew members.
Spock was able to give the coded phrase to the former crew member. This man soon deduced what Spock intended, and sabotaged shipments that the Merkaans were taking by combining it with some chemicals. The shipments were beamed on board the Merkaan ships, and after reacting with the chemicals began to give off gas, which knocked out the crews on all three vessels.
Dreen was stopped from killing Spock, and captured. After his vessels were stripped of their weaponry, and their stolen cargo confiscated Dreen was released. Dreen and his ships soon left the area. Dreen was once again disgraced, and knew that this time there would be no redemption. (TOS novel: Legacy).