Admiral Alidar Jarok was a high-ranking Romulan commander who appeared in the Star Trek: TNG episode The Defector. He is portrayed by James Sloyan.
Around 2366, Jarok argued with his superiors that another war with the Federation would destroy the Romulan Empire, and he became the target of a program of deliberate misinformation by the Romulan High Command, designed to test his loyalty. After dismissing him to command a distant sector, the High Command sent him false communiques, records, and orders concerning the establishment of a secret base on Nelvana III, in the Neutral Zone, in preparation for a massive invasion of Federation space.
Unwilling to allow a war that would devastate both sides, Jarok stole a Romulan scout ship and crossed the Neutral Zone, seeking refuge aboard the USS Enterprise-D. Claiming himself to be "Sublieutenant Setal," he informed Captain Jean-Luc Picard of the offensive. However, Picard was skeptical, given Jarok's reluctance to reveal any Romulan military intelligence beyond the buildup at Nelvana III, which included the self-destruction of his ship. Only after Jarok revealed his true identity and provided the disposition of the Romulan fleet along the Neutral Zone, did Picard order the Enterprise-D to Nelvana III.
When the Enterprise-D reached Nelvana III, they found no evidence of a base whatsoever – only a probe designed to send out a subspace signal and ionization disturbances. Realizing that they had fallen into a trap, the Enterprise-D attempted to retreat, only to be surrounded by two Romulan warbirds commanded by Tomalak. Tomalak revealed the deception, and announced his intention to take the Enterprise-D back to Romulus as a trophy.
Fortunately, Picard had planned ahead and arranged for substantial Klingon forces to follow them under cloak. Suddenly finding himself outgunned, Tomalak withdrew. Jarok, realizing that he had sacrificed everything for nothing, committed suicide by ingesting a felodesine chip. He left only a letter for his family, and the memory of his courage.