Ilonka was a beautiful young girl who was with the gypsies in Frankenstein during Dr. Gustav Niemann and Daniel's visit to the town en route to Visaria. She was a very skilled dancer and earned a great deal of money for her employer, Fejos. But Fejos was a very cruel and selfish man and sought to keep all of the money for himself, and when Ilonka protested, an enraged Fejos brutally whipped her. The sensitive Daniel came to her rescue however and disposed of Fejos, then convinced Dr. Niemann to let him take Ilonka with them on their journey.
Although Ilonka was grateful to Daniel for rescuing her, the hunchback's hideous visage initially frightened her and his romantic attentions were met with pity, not love. Ultimately Ilonka would fall in love with the lycanthrope Larry Talbot, whom Daniel and Niemann had thawed from the frozen bowels of Ludwig Frankenstein's estate along with Frankenstein's Monster. Although the perpetually somber Larry was unresponsive to Ilonka's attentions initially, he eventually warmed up to her and the two became very close (much to Daniel's jealousy).
When Daniel told Ilonka that Larry was a werewolf, she at first assumed the jealous hunchback was merely lying, but she soon learned the truth, that Larry was in fact a werewolf, and sought to end his suffering with a silver bullet fired from a revolver when he transformed into a wolf. This seemed to work (although it was eventually revealed that Larry survived), but before succumbing to the effects of the silver bullet Larry attacked and killed Ilonka.