Karl Marx

The world would not be in such a snarl had Marx been Groucho instead of Karl. The philosophers have only interpreted the world, in various ways. The point, however, is to change it. Karl Marx was the godfather of all pinko commie scum; he co-wrote the Communist Manifesto (with Friedrich Engels) and wrote Das Kapital. He was a philosopher, economist, political activist, and writer, and is considered the grandfather of sociology and political economy.

His ghost subjects Ayn Rand's to eternal wage slavery as she burns in hell.

What Marx did and didn't do
Marx and Engels did not invent the idea of socialism or even communism. There were communist and socialist trade unions and political parties prior to the pair publishing anything on political economy. Additionally, they didn't invent philosophical theorizing about socialism. There were plenty of contemporary thinkers on the topic who published just as many books as Marx and Engels and with whom Marx debated publicly.

Marx was a theory-guy who had little regard for concrete political suggestions. One exception being a single chapter of the Communist Manifesto, where he and Friedrich Engels suggest that advanced countries abolish all private land ownership, implement a progressive tax, do away with inheritance, implement free education, confiscate the property of emigrants and anti-communist rebels, implement heavy state centralization, and make everyone legally responsible to work.

Marx wrote for the New York Daily Tribune, and some believe Abraham Lincoln regularly read his columns, given the language with which the president spoke about the changes then taking place in the American and world economies that he and the radical Republicans were dreading. Marx did, in fact, praise Lincoln for issuing the Emancipation Proclamation and congratulate him on his 1864 reelection and was probably entirely sincere while doing so, which should come as no surprise as Marx regarded wage-earning proletarians as still better off than slaves.

Though he went through a somewhat authoritarian phase in the middle of his life, Marx's work did not advocate anything remotely approaching the authoritarianism advocated and then carried out by Stalin or by Mao. As Marx grew older, he returned to the more libertarian (no, not that kind of libertarian) tendencies of his youth.

Contrary to popular belief, Marx did not create the phrase "from each according to his ability, to each according to his need"; he merely popularized the phrase, which was said to have been originated by in his 1755 book, Code de la nature, ou de véritable esprit de ses lois.

Despite his reputation in certain circles, Marx is perhaps the the most influential economist of the XIXth century. Not because of his impact on economics as a science, where his reputation is largely peripheral, particularly after certain developments rendered his Labour Theory of Value obsolete, but because of his political impact in the development of the communist bloc in the XXth century. By using and  data, economists Phillip W. Magness and Michael Makovi found evidence that the 1917 Russian Revolution is responsible for elevating Marx’s fame and intellectual following above his contemporary competitors. According to them, Marx’s intellectual influence may be partly due to political accidents: the revolution brought attention to Marx, and without it it's quite possible that he would have been forgotten even on academic circles like Sociology.

Ancestry
Marx was of Jewish descent, which was the original prompt by conspiracy theorists to tie Marxism in with the theory of the international Jewish conspiracy, claiming that communism was made to advance Jewish domination of the world (oddly, those clever Joos failed to foresee this and perhaps use a non-Joo to publicly expound upon their great conspiracy). However, Marx's relationship with his Jewish identity is a great deal more complex than all that. His father, Herschel Mordechai, came from a long line of rabbis but received a secular German education himself and converted to Lutheranism around the time of Marx's birth, changing his name to Heinrich Marx. This was a career move; Herschel was a lawyer, but the German government had made it illegal for Jews to practice law. Karl Marx was baptized into the Lutheran church at age six and later in life wrote an essay, On the Jewish Question, in which he drew on stereotypes of money-worshiping "huckster" Jews and stated that as a part of the development of capitalism, "Christians [had] become Jews" (i.e., the "Jewish" culture of capitalism had assimilated all the old cultures of Europe).

Marx and communist states
His fanboys have shown quite a tenacious resistance to the suggestion that something might be wrong with what he said (though given the large split between different factions, to the point where in the Spanish Civil War, Stalinists mostly killed Trotskyists, it is understandable), even as leaders professing his philosophy turn into dictators one after another, and the combined death toll from their regimes rises into the mid-to-high eight figures (largely attributed to Stalinist Russia and Maoist China). One common response to this is to point out that certain anti-communists also racked up non-negligible skull counts in the name of fighting communism, notably Adolf Hitler (and his Axis allies such as Mussolini, Franco, and Pavelic), Suharto of Indonesia, Syngman Rhee of South Korea,, Ngo Dinh Diem of South Vietnam, a succession of military dictators in Guatemala, the junta in El Salvador, the Somozas in Nicaragua, Augusto Pinochet of Chile, Jorge Rafael Videla of Argentina, Hissene Habre in Chad, of Haiti, and  of the Dominican Republic, many of whom were backed by the United States throughout the Cold War. This is an instance of tu quoque, although certain US politicians such as Jeane Kirkpatrick backed anti-communist regimes solely on the basis that they were not as bad as communist regimes, which is debatable as many anti-communist regimes killed an equal or higher per-capita number of those under their control.

However, it is also worth noting that none of Marx's predicted "proletarian revolutions" occurred in industrialized nation-states, such as the United Kingdom where he lived but, instead, in less-industrialized states such as Russia and China during periods of political and economic turmoil. Marx had written that industrial capitalism was a necessary precondition for communism. Marxist rhetoric is also appealing to post-colonial independence movements, even those which are largely agrarian and lacked an established working class. In some cases, such as Yugoslavia, Vietnam, and China, the communist revolutions had popular local support due to the roles they played in war; while in other cases, such as Eastern Europe and Afghanistan, communist governments were largely forced upon them, and such countries essentially functioned as puppet states of the Soviet Union. Of course, forcing a political regime on a largely-unwilling populace does not tend to engender much love and might end a tad bloody. It is also a fact of history that any government will overstay its welcome. If it is the government of a democratic state it will be voted out, If not, too bad.

A frequent argument by Marxists
To get this out of the way, prior to the Russian Revolution (and again after 1991) most Marxists interpreted Marx differently from Lenin. While the non-Leninist interpretation says, basically, that full industrial development under a capitalist system is a precondition for communism (which would make the USSR not a communist state, at least not in Lenin's time), Lenin argued that given the right revolutionary leader (such as himself), a largely-agrarian state (such as Russia) could "skip" capitalism and become communist immediately. Thus, many modern Marxists have explained away the fall and the atrocities of Maoist China (which is now communist in name only) and the USSR as a consequence of their having been largely agrarian at the time of revolution, and hence not "really" communist. Whether this constitutes a no true Scotsman depends largely on your own views on capitalism, communism, and the various Leninist dictatorships.

Darwin and Marx
Karl Marx was deeply interested in the work of his contemporary Charles Darwin. He was an admirer of Darwin and sent copies of Das Kapital, in which he was cited, to him. (Darwin never read it.) Indeed, despite their differences, both theories can be seen as rejections of essentialism, just applied to very different fields. Marx saw Darwin's theory of evolution as a signal that his theories were headed in the right direction: that humankind is the product of historical changes. He wrote in a letter to :

Marx was not uncritical of Darwin, however, and took many issues with his arguments. The notion that Marx and Engels were attempting to co-opt Darwinian evolution for their own political project does not reflect how they related to the theory. Still, at Marx's graveside, Engels remarked, “Just as Darwin discovered the law of development of organic nature, so Marx discovered the law of development of human history.”

Marx's bigotry
Those who read Marx in depth will notice the repeated and sometimes extreme prejudice involved in his insults and general opinions. Many modern Marxists try to deny his racism. It should, of course, be remembered that everyone is a product of their time. After all, Marx's philosophy emphasizes the influence of material and historical conditions influencing people's lives, and the man himself was no exception. Marx exposed deep prejudices in both personal letters and in his published writing. He expressed numerous horrendous comments on Slavs, ‘Negroes’, Bedouins, Jews, Chinese and many others. He also appeared to have fallen for the pseudoscience of phrenology as well.

The most controversial of his bigotries was Marx’s antisemitism. Despite his Jewish heritage, Marx didn’t identify as a Jew and wasn’t raised as one. He went on to write disdainful comments on Jews throughout his career. "On the Jewish Question", in which he argues against Bruno Bauer that a secular state would not emancipate people from their material conditions, is often considered his most antisemitic work. In it, he makes statements that describe Jews as money-grubbing hucksters, and how these ascribed temperaments relate to capitalism. Some scholars claim Marx was not antisemitic, and that he was being sarcastic, or that he wasn’t that bad. Others claim that this allegation comes from an anachronistic or superficial reading of "On the Jewish Question". More antisemitism can be found in further writings and correspondences. He described Jews as greedy and once referred to them as “leper people.”

Like virtually all Europeans of his era, Marx viewed those of African ancestry as more primitive than most other races. For example, he said Black people were “a degree nearer to the rest of the animal kingdom than the rest of us” and he referred to people with racial epithets. Despite his racism, Marx was also in favor of the abolition of slavery.

Marx wrote that he distrusted Russians and generally disdained Eastern Europeans. Marx was also sort of pro-imperialism, seeing it as a natural and necessary stage in the evolution of world political economy. He wrote that he felt England had a duty to annihilate “old Asiatic society” in India. When it comes to Chinese people, Marx criticized them, claiming that "It would seem as though history had first to make this whole people drunk before it could rouse them out of their hereditary stupidity".

The good

 * Support for and instances of worker self-management are growing throughout the world. A number of Western and Latin American countries have adopted policies aimed to produce and support employee-owned firms. Other countries, such as Great Britain and Spain, are simply waiting to elect their left-wing parties to a majority in their parliament before doing so. Bernie Sanders included the idea on his platform, but never brought it up during his campaign; he also never became POTUS, the poor bastard.
 * The threat of Marxist revolution scared a lot of governments into making positive reforms for the working class. People in power generally don't make concessions to people without power out of the goodness of their hearts...

The neutral

 * Marx is still taught and studied in academia, and his influence is still felt in the study of sociology, political science, philosophy, and more.
 * Marx's political theories have become increasingly popular with Milennials and Gen Z.

The bad

 * A hefty amount of strongmen from the "somewhat tolerable if you're desperate" to the "unfathomably horriffic" have justified their abuses by referring to his work. It happens too often when Marx-derived ideologies are implemented to be a regrettable coincidence.
 * The spread of reformist ideologies like Social Democracy has rendered his central thesis—the only way to improve lives for the bottom half of society is armed revolution—to seem less relevant in the modern day.
 * Tankies still exist on the fringes of society in the present day.

Marx versus Marxists
Whatever you may think of Marx and his fanclub, he did at the very least condemn the fanaticism when he witnessed it. A rather famous quote of Karl Marx reads:

He said this in reaction to Jules Guesde, a leader of French workers and vanguard of French Marxism, who visited Marx in London 1880. They had a disagreement about the political programme written for the Parti Ouvrier (Labour Party), in what seems to be the case in which Marx was in favor of pragmatic achievements within capitalism while his cult didn't want any reasonable concessions but just concern-troll the opposition (Marx called it "revolutionary phrase-mongering"). As a joke question: Would Marx oppose Bernie-or-Bust?