She was intended for a major role in The Undiscovered Country, but between casting difficulties and objections by Gene Roddenberry over an established character becoming a traitor, her name was simply used as a placeholder for Kim Catrall's character, Valeris.
Foil: To David Marcus. Both are younger men subordinate to an older man who acts as a parental figure to them, but while David is brash and wants nothing to do with Kirk (at first), Joachim is reserved and has Undying Loyalty to Khan.
While the film leaves it ambiguous whether Joachim is meant to be Khan's son or not, the Expanded Universe explains he's his adopted son, raised by Khan after his parents (his father being Joaquin from "Space Seed") were killed in battle.
Only Sane Man: Granted, he's the only speaking member of Khan's crew so we never really find out what his other followers think, but he's certainly the only one who actually stands up to Khan.
Mook Lieutenant: Not really physically intimidating to be The Dragon, as Khan does all his own interrogations. He just exists to allow Khan to awesomely monologue to someone.
Morality Chain: Joachim tries to be this to Khan, but it doesn't really take.