Thomas Midgley (1889-1944), the American engineer and inventor. Working for Delco in World War I, he led a team working on 'knocking' in petrol engines. He found that tetra-ethyl lead (when used with 1,2-dibromo-ethane to reduce lead oxide deposits in the engine) is highly effective at reducing knocking when added to petrol. The mixture is still used as an anti-knock additive today. Midgley also devised the octane number method of rating petrol quality. In 1930 he introduced Freon 12 as a non-toxic non-flammable agent for domestic refrigerators. Both his main discoveries have since been implicated with environmental problems.