Trotsky was born Jewish but became atheist to reconcile with his Marxism.
Leon Trotsky was born in what's now Ukraine in 1879 in a relatively wealthy Jewish household. He was assassinated in Mexico by a Soviet agent in 1940.
Trotsky is a Marxist. To many Marxists, the philosophy is comprehensive, encompassing everything from a philosophy of society, history, religion, aesthetics, politics to economics–and possibly even more.
Religion is not something Marxists are too fond of. There are hundreds of quotes from Marxists about religion. Here's one of Trotsky's:
Religions are illogical primitive ignorance. There is nothing as ridiculous and tragic as a religious government.
Not only was he opposed to religion in government and thought that religion was, as Marx put it, "the opiate of the masses," he was simply an atheist.
His own kind of communist
Trotsky was–politically, economically, and socially–a communist. He was instrumental in the Bolshevik revolution of 1917 in Russia which installed a Communist government for the next 72 years.
He was a champion of the proletariat, and enemy of the bourgeois. But even though he was a very high-ranking member of Russia's communist party–barely losing out as leader to Joseph Stalin–he had his own unique ideas on Communism, ideas that resulted in his exile from Russia and eventual assassination, but also ideas that garnered him many followers even to this day.
For one, Trotsky realized that Democracy was important and was critical of the Russian communist bureaucracy and fascist leanings. He opposed the fascist governments of Germany and Spain during his time and urged Stalin to wage war on Nazi Germany–which he eventually did. Of fascism, he said:
Fascism is nothing but capitalist reaction.
If you're a communist, that's a pretty big insult.
For his high position, Trotsky seemed to never lose his idealistic streak. Where Lenin and Stalin abused their power in Russia, Trotsky continued to push for a true government of the workers rather than one ruled by elite party members–which Russia quickly became. He said:
Ideas that enter the mind under fire remain there securely and for ever.
And they certainly remained with Trotsky until the end.