Karl Marx's work "can be explained in five minutes, five hours, in five years or in a half century," wrote French political thinker Raymond Aron.
A utopian vision of a just society for some, a blueprint for totalitarian regimes for others, Marxist thought is laid out in the Communist Manifesto and the three-volume Das Kapital.
But, Marx wasn't just the intellectual who inspired some of the cruellest despots of the 20th century. He was also a man who liked a drink and a duel - and who wasn’t impartial to taking a bit of cash from the dastardly industrial classes.
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Figure of fun
Marx was born in Trier in 1818 and spent the first 17 years of his life in the town near the French border.
The family had a long connection to Trier, as the position of city rabbi had more or less been passed down his paternal line since 1723. His father, Heinrich, was the first to break with this tradition by becoming a lawyer.
Jews were still oppressed in the Prussian empire during the early 19th century and Heinrich converted to Protestantism in order to be able to practise law. Heinrich was himself something of a rebel - the Prussian authorities kept an eye on him due to his membership of the Casino Club, an organization that extolled the virtues of the French enlightenment.
Marx apparently never shook off his thick Trier accent, which made him a figure of fun for jealous intellectuals in his later life in Berlin and Cologne. The fact that he also had a lisp didn’t exactly help his case.
In his early student days in Bonn, he seemed to spend most of his life getting drunk and fighting. He was a member of the Trier Tavern Club at the uni and got into the habit of carrying a pistol after club members kept getting attacked by the Borussia Korps, reactionary supporters of the monarchy. Eventually he ended up duelling one of the Borussia gang.
Wrote a novel as a student
As a 19-year-old, Marx tried his hand at being a novelist with the book Skorpion und Felix, Humoristischer Roman. He was studying law in Berlin at the time and the book appears to have been an outlet for his real passion - philosophy. Marx experts have variously described it as a veiled philosophical discussion with Hegel, Kant and Locke.
But the unfinished book wasn't supposed to be very good - even Marx apparently wasn’t convinced by its literary merit - he burned parts of it, meaning only fragments now survive.
Marx finished his studies in Berlin in 1841, but actually submitted his doctoral thesis to the University of Jena. The thesis was predictably controversial - it declared the primacy of philosophy over religion - and he thought it would get a better hearing at the liberal Jena than at Berlin's conservative university.
He also managed to shock fellow students by riding a donkey drunk through the streets of Bonn and a trip to the town.
Married an aristocrat
While he may have been on the side of the proletariat in word, in love Marx still stuck by the class of capital. In 1843, after years of engagement, he married Jenny von Westphalen, the daughter of a high ranking Prussian noble.
Von Wetphalen, by the way, had the patience of a saint. Not only did she traipse around Europe as her husband was expelled from one country after the next, she also had seven children while doing so. And she put up with him having an illegitimate child with their housekeeper.
Marx’s mother was also from a family of Dutch industrialists who went on to establish the Phillips electronics company. While in exile in London, he often relied on loans from a rich uncle who had his own tobacco company.
Ran a Cologne newspaper - for a while
Marx was the editor of the Rheinsiche Zeitung in 1842. He was so successful in the role that the newspaper’s circulation doubled in a year. It was while Marx was in charge of the paper that he first met Friedrich Engels, who was a member of a left-wing intellectual circle in Berlin.
Unfortunately for Marx, he was a little too good at being a newspaper editor - the publication was banned shortly afterwards.
The reason for the ban was an article strongly critical of the Russian Tsar Nicholas 1. The Russian monarch requested that the newspaper be banned and the Prussian authorities complied.
Tried to run another newspaper in Cologne
After living in exile in Paris and Brussels for five years, Marx returned to Cologne in 1848 to have another bash at being a journalist. This time he set up the Neue Rheinische Zeitung. Frierdich Engles reportedly observed that, although many other communist intellectuals worked there it remained “a simple dictatorship by Marx.”
Within a year the reactionary Prussian authorities had again had enough of the outspoken intellectual. This time they shut down the newspaper and booted him out of the country.
"The history of all hitherto existing society is the history of class struggle," says the Communist Manifesto, co-written with Friedrich Engels and published in 1848.
Marx believed that humanity's core conflict rages between the ruling class, or bourgeoisie, that controls the means of production such as factories, farms and mines, and the working class, or proletariat, which is forced to sell their labour.
According to Marx, this conflict at the heart of capitalism -- of slaves against masters, serfs against landlords, workers against bosses -- would inevitably cause it to self-destruct, to be followed by socialism and eventually communism.
'Dictatorship of the proletariat'
This idea -- coined by early socialist revolutionary Joseph Weydemeyer and adopted by Marx and Engels -- refers to the goal of the working class gaining control of political power.
It is the stage of transition from capitalism to communism where the means of production pass from private to collective ownership while the state still exists.
The concept, including suppressing "counter-revolutionaries", was proclaimed by the Russian Bolsheviks in 1918.
Vladimir Lenin wrote that it is "won and maintained by the use of violence", signalling the authoritarian drift that began after Russia's 1917 October Revolution.
Marx and Engels wrote the "Manifesto of the Communist Party" in 1848, at a time of revolutionary turmoil in Europe.
It only reached a wide readership in 1872 but became part of the canon of the Soviet Bloc in the 20th century.
For Marx, the goal was the conquest of political power by workers, the abolition of private property, and the eventual establishment of a classless and stateless communist society.
According to Marx's theory of historical materialism, societies pass through six stages -- primitive communism, slave society, feudalism, capitalism, socialism and finally global, stateless communism.
In reality, the abolition of private property and the collectivisation of land resulted in millions of deaths, especially under Russia's Joseph Stalin and China's Mao Zedong.
"Workers of the world unite!" is the famous rallying cry that concludes the Manifesto and seeks to create a political structure that transcends national borders.
The idea lay at the heart of Soviet internationalism, uniting the destiny of countries as geographically distant as the USSR, Vietnam and Cuba, and revolutionary groups including the Colombian FARC or the Kurdish Workers' Party PKK, as well as anti-globalisation movements.
'Opium of the people'
Marx believed that religion, like a drug, helps the exploited to suppress their immediate pain and misery with pleasant illusions, to the benefit of their oppressors.
The quote usually paraphrased as "religion is the opium of the people" originates from the introduction of Marx's work "A Contribution to the Critique of Hegel's Philosophy of Right".
In full, it reads: "Religion is the sigh of the oppressed creature, the heart of a heartless world, and the soul of soulless conditions. It is the opium of the people."
The idea was used to justify brutal purges of religions in Russia, China and across eastern Europe.
Some scholars point out that Marx saw religion as only one of many elements explaining the enslavement of the proletariat and may have been surprised to see radical atheism become a core tenet of communist regimes.