From wikipedia:
James Warren "Jim" Jones (May 13, 1931 – November 18, 1978) was the American founder of the Peoples Temple group, which became synonymous with group suicide after the November 18, 1978 mass murder - suicide by poison in their isolated agricultural intentional community called Jonestown, located in Guyana. Nine hundred and thirteen (913) people drank cyanide after Jones ordered his men to kill visiting Congressman Leo Ryan and numerous members of his entourage.
Supposedly, the cyanide was mixed with kool-aid or some such drink.