The Genophage is a fictional biological weapon from the video game series Mass Effect. It was developed by the Salarians and used against the Krogan species to control their population. The Genophage causes severe infertility, drastically reducing the number of Krogan births and leading to a significant decline in their population over time. The Genophage was created in response to the Krogan's rapid expansion and aggressive behavior, which posed a threat to other species in the galaxy. While it successfully limited the Krogan numbers, it also resulted in long-lasting social and political consequences, contributing to the Krogan's struggles for identity and survival.