In 2372, Captain Kurn, the commanding officer of the IKS Hegh'ta and the younger brother of Regent Worf, allied himself with Drex in an effort to gain command of the new Regent-class ship IKS Gorkon. When Kurn learned of a betrayal of the Alliance by the House of K'Tal, he tried to turn this to his political advantage. However, Commander Klag of the IKS Pagh also learned of this treachery and, due to his heroic actions to reveal it, was granted command of the Gorkon instead. Kurn, in turn, was given command of the IKS Ya'Vang. Drex became the first officer of the Gorkon.
Shortly after their respective proportions, Kurn sent Drex a message instructing him to observe Klag carefully for any sign of weakness and to "strike like a wam serpent" if one becomes apparent. Although Klag had recently earned his brother Worf's favor, Kurn assured Drex that, should he kill Klag, he would be protected as he was the son of Martok. (KE - Mirror Universe short story: "Family Matters")
After Worf was captured by the Terran Rebellion in 2375, Drex's father succeeded him as the Regent of the Klingon Empire, serving in that position until he was slain in honorable combat by Klag in 2377. (DS9 novel: Warpath; ST - Mirror Universe novel: Rise Like Lions)