Klingon who was also Romulan spy. J'Dan, an exobiologist, served aboard the U.S.S Enterprise-D as part of the Officer Exchange Program in 2367. During that time, he stole dilithium crystal articulation frame designs. These designs were smuggled off the ship in J'Dan's bloodstream, the designs transferred to amino acid molecues. When confronted with evidence of his actions, he confessed.