Poison Ivy appears in 749 issues.
A botanical biochemist, Pamela Isley is a fervent eco-terrorist out to save the world's plant life by any means necessary. She often finds herself at odds with Batman, though they have, on occasion, fought on the same side. Pre-New 52 she had a long friendship with Harley Quinn and, in fact, gave her meta-human abilities. Ivy, Harley, and Catwoman later teamed up as the Gotham City Sirens. Post-New 52, she was a member of the Birds of Prey for a time before betraying them to further her cause.