Bayer AG is a chemical and pharmaceutical giant founded in Barmen, Germany in 1863 by Friedrich Bayer and his partner, Johann Friedrich Weskott.
Today it has its headquarters in Leverkusen, North Rhine-Westphalia, Germany. It trademarked acetylsalicylic acid as aspirin in 1899.
It also trademarked heroin a year earlier, then marketed it world-wide for decades as a cough medicine for children "without side-effects", despite the well known dangers of addiction.
During the First World War, Bayer turned its attention to the manufacture of chemical weapons including chlorine gas, which was used to horrendous effect in the trenches. It also built up a "School for Chemical Warfare".
During this time Bayer formed a close relationship with other German chemical firms, including BASF and Hoechst.
This relationship was formalised in 1925 when Bayer was one of the chemical companies that merged to form the massive German conglomerate Interessengemeinschaft Farben or IG Farben, for short.