Dr. Gevaarlijk is a professor of evil science from Drusselstein. She is very short with blond hair and wears glasses. She was a teacher of Dr. Heinz Doofenshmirtz when he took Evil Science 101. She hated and tormented him when he was her student. The doctor openly despised him, yet Doofenshmirtz still wanted to impress her.
Doofenshmirtz wrote her a letter inviting her to Danville to impress her with the enormity of his evil schemes. He tried to show off his inventions and his nemesis, Perry the Platypus who did not do anything. Also in honor of her visit, he planned to blow up the moon with an unnamed laser device to stop all songs about it. She approves of this plan since she, too, despises moon-related songs. Unfortunately, the plan backfires when he leans on the laser and redirects it towards a nearby dam. Because she enjoys a good toe-tapping dam song, she is even less impressed with Doofenshmirtz's schemes.
In the end, she tells Doofenshmirtz that evil doesn't always have to be on a large scale. He could just spread evil in the little things he does everyday, but that he can't even do that. ("Oil on Candace")
Gevaarlijk is a Dutch word meaning "dangerous." (ref) This, plus her accent, means she is likely Dutch. However she also has an accent in the Dutch episodes of Phineas and Ferb, The accent is German-like.
When subtitles is on during the episode, Gevaarlijk is spelt Hevarlick.
It is unknown if Dr. Gevaarlijk failed Doofenshmirtz because she hated him, or she hated him because he failed.
In one scene, she suddenly got four eyebrows, but they vanished in the same scene.