Joachim is the secondary antagonist in the film Star Trek II: The Wrath of Khan.
He was portrayed by Judson Scott.
Joachim was one of the genetically engineered supermen who was exiled on Ceti Alpha V with Khan Noonien Singh. Like the others, he was fiercely loyal to Khan. When their encampment was mistakenly discovered by Captain Terrell and Commander Chekov of the USS Reliant, the group had a chance to escape. Infected the pair with eels that forced them to do their bidding, they hijacked the Reliant, stranding most of the crew on the planet.
Joachim served as Khan's right hand in his control of the ship, as well as acting as pilot. Khan had too remaining goals: To gain control of Project Genesis and to get revenge on Admiral Kirk. Despite his loyalty, Joachim questioned the wisdom of Khan's actions, arguing he had already defeated Kirk by escaping from exile. However, Khan shut down the argument by insisting he would always be troubled while Kirk remained alive.
Having raided the Regula I station where Genesis was being constructed and killed most of the scientists, Joachim piloted the Reliant as it attacked the Enterprise and badly damaged it. However, the Reliant also suffered damage when Kirk forced it to lower shields and Joachim convinced Khan they should withdraw and conduct repairs. They used the brainwashed Terrell and Chekov to locate the Genesis probe and beamed it aboard.
Returning to attack the Enterprise, Khan, Joachim and the others found it in better shape than expected. Nevertheless, the Enterprise retreated towards the Mutara Nebula. Joachim attempted to pull back rather than following them in, but when Kirk taunted him, Khan pushed Joachim aside and entered the nebula. With sensors scrambled by the interference and Khan's crew inexperienced in starship command, the Enterprise was able to ambush the Reliant and rake it with phaser fire, badly damaging the bridge. Joachim was fatally injured in the attack and died in Khan's arms.
In Khan's previous appearance, "Space Seed", his right hand man was called Joaquin, although he appeared to be the same age as Khan, not notably younger as Joachim was. The novel To Reign in Hell: The Exile of Khan Noonien Singh makes Joachim the son of Joaquin, who died on Ceti Alpha V.