Novichok

The name Novichok is used for a number of chemical compounds that have been used as nerve agents (similar to nerve gas) from the 1970s to at least the 1990s in the Soviet Union. There are 3–5 different substances, all called Novichok. The exact formula of these agents is unknown. The following facts are known or likely:
In 2018, former Russian spy Sergei Skripal and his daughter were poisoned using Novichok. Novichok was also the agent in the 2018 Amesbury poisonings. It is likely that Alexei Navalny was poisoned using Novichok in 2020.