In 2267, he was one member of the first Enterprise landing party sent to the surface of Pyris VII. The Enterprise lost contact with this landing party until, about a half-hour after it was overdue, Jackson called the ship and requested a one person beam-up. He was beamed to the ship, where Kirk was prepared to question him about the fate of the rest of the landing party, but when he materialized, he was dead.
Kirk later learned that Sylvia had killed him using a science she likened to sympathetic magic; she constructed an image of him in her mind, and when she knew that it was dead, Jackson died. Korob used Jackson's dead mouth to warn Kirk; his sonorous voice told Kirk there was a curse on the Enterprise, and that it should leave immediately, or everyone aboard would perish. (TOS: "Catspaw")