Leaded gas was introduced in the 1920s despite being a known poison, with General Motors engineer Thomas Midgley Jr. discovering its use as an anti-knock agent. The use of leaded gas had dire consequences, including lead poisoning and environmental contamination. It wasn't until the mid-1970s that the EPA began to phase out leaded gasoline due to growing evidence of its dangers. The effects of leaded gas are still being felt today, with ongoing environmental and health impacts.