The assassination of Leon Trotsky was ordered by Joseph Stalin circa 1939. After one failed assassination attempt in Mexico (where Trotsky was living) in March of that year, Stalin turned to NKVD (Russian Secret Police) agent Pavel Sudoplatov to finish the job. Sudoplatov and the NKVD set up three assassination teams operating autonomously from all other NKVD spy networks. The first effort by this group was again unsuccessful, Trotsky's guards were able to fight them off. The next effort, three months later on August 20, 1940, was successful. The assassin was Ramon Mercader, using an ice axe. Even this third attempt was partially bungled, as Trotsky didn't die immediately but survived for more than a day, and Mercader was captured.

Leon Trotsky joined the Bolsheviks just before the 1917 Russian Revolution and immediately became a member of the Communist Party leadership, earning several high positions. After leading a failed struggle against Lenin and the expanding Soviet bureaucracy he was expelled from the party in 1927. Continuing to oppose Lenin's successor, Joseph Stalin, he continued the fight from exile, leading almost inexorably, to his assassination.

Mercader, the Spanish born assassin, served 20 years in a Mexican prison for his deed, and was awarded the "Order of Lenin" by Stalin in absentia.

More Info: en.wikipedia.org