Dr. Gevaarlijk was a minor villain in Phineas and Ferb, only appearing in the episode Oil on Candace.
She was a teacher who previously taught Heinz Doofenshmirtz at Evil Science 101, though she openly hated him for unknown reasons. Despite this, he tried to impress her with his countless -inators. This doesn't win her over, however. During her visit at Doof's he later tries to show her that he's truly evil by presenting his nemesis Perry the Platypus. Unfortunately, Perry's reverted back into his "mindless pet form." Doof tries to honor her visit by blowing the moon with a laser he invented, since Gevaarlijk actually despised moon-related songs. Finding this to be impressive, Gevaarlijk allows Doofenshmirtz to continue, but he accidentally used the laser to destroy a dam, much to Gevaarlijk's disappointment (as she liked a dam-related song). She seemed to reassure him saying that he could try being a bit evil everyday. Doof is touched, but Gevaarlijk also states that he couldn't even do that right, and that he was an absolute failure. She then furiously leaves, leaving Doof hopeless, though he would later be cheered up by Perry for his efforts of trying to assert evil.
- Despite Gevaarlijk declaring Doofenshmirtz to be a total failure, there were a few times when Doofenshmirtz actually succeeded in his schemes, such as moving the Earth away from the Sun to an early autumn in Phineas and Ferb Save Summer, and when he got elected as the First Tri-Governor of the Tri-State Area in Last Day of Summer. This may indicate that Gevaarlijk may be wrong about him.
- Her name means 'dangerous' in Dutch.