In 1999, Hoechst merged with Rhône-Poulenc to form Aventis.
Hoechst AG was founded near Frankfurt in 1863 as a German dyestuffs manufacturer. It expanded from industrial chemicals into pharmaceuticals and life sciences, becoming one of Germany's most important chemical groups. Its earlier history included participation in IG Farben, the large chemical combine formed in 1925, before Hoechst was re-established as an independent company after the Second World War.
The cross-border merger with France's Rhône-Poulenc was completed in January 1999. The new group, Aventis, combined Hoechst's pharmaceutical and chemical operations with Rhône-Poulenc's medicines and agricultural-chemicals businesses. It was one of Europe's major pharmaceutical companies and operated internationally across prescription drugs, vaccines, crop protection and other life-science markets.
Aventis did not remain independent indefinitely. In 2004, it merged with Sanofi-Synthélabo to create Sanofi-Aventis; the group later dropped “Aventis” from its name and became Sanofi. The merger partner is also sometimes described as Rhône-Poulenc S.A., but Hoechst remains the single canonical answer.