Dr. Wu was a doctor at a Gotham City hospital.
History
When Batman found a crook hallucinating, he left her in the care of Dr. Wu. She ran some tests on both the thug and Batman, and found the Dark Knight had been exposed to the same toxins. But because he breathed in less of the gas, it took longer to become effective. Driven by the need to hunt down the toxin's originator, Batman ignored Dr. Wu's advice for rest, and her medication.