Joseph Stalin gained total control of the Soviet Communist Party and of the Soviet Union. Trotsky was a true communist and political rival of Stalin. Leon Trotsky and his family were exiled and after that, Stalin decided that Trotsky was still a "thorn" in his side and so offered a huge reward for the assassination of Trotsky. He was killed in Mexico.
Chuck Siata here to say I made a minor edit. First answer is from Trisanhg90.
Leon Trotsky was killed by Ramon Mercader, who was an agent of the NKVD, the Soviet Internal Affairs Department on August 20, 1940. He was severely injured by an ice ax that hit him and died of trauma a day later died in the hospital after surgery.
Previously, the USSR had attempted to kill him, but with no success until then.
Ramon Mercader, likely an agent of Stalin
The KGB was not around until after Stalin's death. The story is that Stalin had some an agent of the NKVD - the Peoples Commissariat for Internal Affairs, a public secret police system under Stalin notorious for running the Gulags - named Ramon Mercador, from Barcelona Spain. This man claimed to have been born in Tehran under a diplomat for a father, and was a Belgian journalist named Jacques Mornard who bought a fake passport on the black market. The man was released in prison after 20 years in 1960 and went between Cuba and the USSR (where he was apparently treated like a hero.) He was never able to get back to Spain fortunately, even though he wanted to.
As an aside, reportedly Stalin placed a bounty on Trotsky's life. Some say it was $1 million others say it was $100,000.
On August 21, 1940, Russian agent Ramon Mercader killed Leon Trotsky in his home in Mexico City, Mexico using an ice axe.
Trotsky was killed by a Russian agent named Ramon Mercader.
Trotsky was killed with an ice axe, not a simple ice pick.
Mexico
Leon Trotsky was a good leader of the revolution.
Leon Trotsky was murdered in 1940.
Trotsky was killed by a Russian agent named Ramon Mercader.
Trotsky was killed with an ice axe, not a simple ice pick.
Leon Trotsky was killed years before 1977 by an assasin sent by Stalin. Stabbed him once in the neck with an ice pick.
Mexico
Leon Trotsky was a good leader of the revolution.
Leon Trotsky was murdered in 1940.
Vladimir Lenin and Leon Trotsky.
A Soviet Politician by the name of Leon Trotsky was killed on 21/08/1940 with an ice pick.
Leon Trotsky died on August 21, 1940 at the age of 60.
Trotsky was murdered in Mexico.
He was killed in his home (in Coyoacan, Mexico city) in 1940. His death was caused by an icepick being smashed into his skull.
After spending imprisonment in Siberia, Leon Trotsky was allowed to live, by Stalin. Trotsky began his exile in Turkey in Alam Ata.