She was the Snake Goddess wife of KASYAPA, who also had another wife VINATA. There was great jealous rivalry between them. KADRU asked for a thousand children, and amongst them were SHESHA and VASUKI. VINATA asked for just two children, with the stipulation that they must outrank those of KADRU. The two children were VARUNA and GARUDA.
Thwarted, KADRU took to crawling into the wombs of pregnant women who then produced more snakes, or worse, humans with snake-like propensities such as cold-blooded cunning and evil.
This is why we have so many people with these characteristics slithering about the world today. Many seem to go into politics and seek positions of power. For protection against this sort of thing you need GARUDA.