On 20 August 1940, Leon Trotsky, a Russian revolutionary, Soviet politician, and political theorist living in exile, was fatally attacked at his residence in Mexico City by Ramon Mercader, a Spanish-born agent of the Soviet secret police (NKVD). At around 17:20 local time, Mercader struck Trotsky in the study with a mountaineering ice axe. The wide end of the axe fractured Trotsky's parietal bone and penetrated about 7 cm into his brain. The blow did not kill him instantly; witnesses said Trotsky struggled with his attacker, breaking Mercader's hand, before bodyguards burst into the room. Trotsky was taken to a nearby hospital and operated on, surviving for more than a day, and died on 21 August 1940 at age 60 from blood loss and shock.
The killing followed an earlier attempt. On 24 May 1940, armed assailants raided Trotsky's villa; his 14-year-old grandson, Vsevolod "Esteban" Volkov, was shot in the foot, and a young assistant and bodyguard, Robert Sheldon Harte, disappeared with the attackers and was later found murdered. The source account states it is probable that Harte was an accomplice who admitted the raiders. Trotsky's other guards repelled the attack. On 8 June 1940, Trotsky published an article, "Stalin Seeks My Death," in which he stated that another attempt was certain. According to the account, the operation to kill Trotsky had been organized by the NKVD after an earlier plan failed in March 1939 and formed part of a broader campaign to infiltrate Trotskyist networks in the United States and Europe.
By 27 August 1940, an estimated 300,000 people had passed by Trotsky's funeral casket in Mexico City. Mercader was tried and convicted of murder and served 20 years in Lecumberri Prison in Mexico City. Soviet leader Joseph Stalin publicly denied responsibility and dismissed Mercader as a Trotskyist, while, per the account, Mercader's mother received the Order of Lenin for her part in the operation. After his release in 1960 and resettlement in the Soviet Union in 1961, Mercader was awarded the Order of Lenin and named a Hero of the Soviet Union. In May 1975, the International Committee of the Fourth International launched "Security and the Fourth International," an inquiry into the assassination and the infiltration of the Trotskyist movement by Soviet intelligence agents.