Magda Kovacs is one of three women whom Harcourt Mudd was taking to Ophiucus III as wives when the USS Enterprise intercepted him. Originally from the Halium experimental station, her prospects for marriage were not good despite her beauty, and so she agreed to Mudd's plan. Mudd introduced her to the Venus drug, a chemical that increased her natural beauty and allure to almost supernatural levels – or so she thought.
As part of Mudd's plan to extricate himself from various charges filed against him, she used her allure to learn how to reach the miners on Rigel XII, and to obtain a communicator. Mudd was able to reach the miners first, and so Kirk was forced to take her and the other women to Rigel XII, as part of his attempts to obtain vitally needed lithium crystals.
The miners were enchanted with these women, and Magda was one of two who married a miner via subspace radio marriage, before Ben Childress learned that their allure had been enhanced.