Thundering Engine Woman was the name of one of the Heterodyne Boys' travelling companions, a very strong Spark from the Americas. An article by Boris Dolokhov reproduced in the fourth issue of the original Girl Genius comic noted that she visited Europe, and travelled with the Heterodyne Boys, for a period of time shortly before the Other War. In this article, it is also noted that there were only a limited number of Sparks in the Americas, but they were powerful ones, and that she was the most famous of them. She is also said to have spoken of the presence in the Americas of forces that were much more powerful than herself.