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Rodrigo "Rod" Mendez was a Human Starfleet officer. He was the elder brother of Commodore José Mendez, commander of Starbase 11. He was married and had one son, Yoshi Takhumara.

In 2249, Mendez and his family were onboard the transport ship Brass Ring when it was attacked by the Romulans, resulting in the death of his wife, and leaving Mendez desirous for revenge against the Romulans. Twenty years later, in 2269, he held the rank of admiral and was head of weapons research at Starfleet Command. Around this period, Mendez and several other admirals formed a clandestine group devoted to developing bioweapons against the Romulans, and centered their efforts at the secret research base on the planet Tanis. Yoshi was one of the researchers assigned to that base, as was Dr. Jeffrey Adams, another survivor of the Brass Ring.

Late in 2269, Tanis issued a distress call. The USS Enterprise sent a landing party to investigate to find the other researchers dead, and Adams infected by an unknown virus; a delayed message from Mendez ordered the Enterprise not to answer the distress call. The Enterprise's senior officers - Captain James T. Kirk, Commander Spock and Dr. Leonard McCoy - were suspicious of this, as the Tanis base used Starfleet-issue technology, and both Spock and McCoy suspected the base was used for bioweapons research. Despite Kirk's questions, Mendez demanded that Adams be brought to Starbase 9; Adams, after attempting to escape, confessed that he worked for Mendez, and that he feared the admiral would kill him if he was turned over to his custody. When questioned by Kirk (who thought the elder Mendez looked something like a bully) about the seemingly personal nature of his desire for justice against Adams, Mendez admitted that Yoshi had been his son.

Despite the apparent guilt of Dr. Adams, Kirk called on an old friend at Starfleet Headquarters, Rear Admiral Quince Waverleigh, to see if he could find any evidence to Adams' claims of Mendez being involved in a clandestine bioweapons operation. Despite early appearances that Adams' story was untrue, Waverleigh eventually discovered that there was indeed a conspiracy at Starfleet Headquarters, but was killed in a skimmer accident in San Francisco Bay shortly after sending an anonymous warning to Kirk. By that point, Adams had escaped from Mendez's custody and returned to the Enterprise, which was making its way back to Tanis to locate the original virus - the one designed for Romulans. However, Mendez and one of his cohorts confronted Spock and McCoy in the base, and threatened to destroy the Enterprise if they did not give him the sample. The Starfleet officers were then beamed onto a Romulan Bird-of-Prey summoned by Dr. Adams using a stolen communicator; despite the accusations against him, Mendez offered his knowledge of Romulan ships to disable the ship's shields and return to the Enterprise. When they did, the Romulans fired on them; Mendez recovered a dropped phaser before either Spock or McCoy could, and demanded that Adams and his virus sample be brought to him.

Captain Kirk brought Adams in a containment suit, condemning Mendez for his involvement in the matter (and possibly in Admiral Waverleigh's death). Mocking the admiral's lack of planning, Adams approached Mendez and lowered the forcefield around his suit, despite Mendez's begging to keep him away, fearing he was infected. Finally breaking as Adams touched him on the arm, the admiral collapsed, sobbing to the deck; unbeknownst to him, however, Adams had been cured of the disease. Mendez was then taken into custody, pending court-martial. (TOS novel: Bloodthirst)