What defines Victor Frankenstein as a mad scientist?in his reasons for creating his monster, his reaction to his monster after it is animated and his later view of the dangerous pursuit of knowledge
Victor Frankenstein (and Robert Walton, for that matter) are driven by the same "illness"--they want to do something than no man has done before. They want to be recognized as amazing and wonderful in the annals of history. Victor's ambition is rooted in his science and his desire to discover a way to bring loved ones back from the dead (he is spurred on to do this also by the effect the death of his mother has on him). Walton's ambition is to discover a passageway through the Artic which is why he happened to be in the path of Victor and the creature in the pursuit at the end.
While Victor is creating his creature making him "beautiful" with his black lips and yellow skin which stretches over an 8-foot tall frame, he is focused and disillusioned. He thinks of the creature as his ticket to fame and therefore is in love with him. Once the creature is alive, Victor realizes how ugly and repulsive the creature actually is. He runs from the creature and falls into a deep sleep induced by months of neglect and malnutrition. When he awakes to see the creature peering in through the bedcurtains at him, Victor shrieks and flees his creation. Victor spends the night wandering the streets and hoping the creature will just go away.
After the deaths of Henry, William, Justine, his father, and Elizabeth that Victor finally realizes his ambition was not worth the cost. He tries to teach Walton this lesson.
The notion that a man regardless of his pursuit of "science" decides that he has the right or even the capacity to play "God" pushes him into the realm of a "madman". It is reasonable to conclude that experimenting the way Frankenstein did had serious consequences. Consequences so radical their outcome is inconceivable to mere mortals. This theme grows in its intensity through out the novel.The terminology of "mad" scientist embodies the idea that perhaps there are certain realms, no matter how genius the scientist, that humanity has no business trying to master or control.