Engels created Marxism by theoretical errors he himself admitted to overemphasizing. Lenin fully embraced and expanded those mistakes, Stalin took them to an even more extreme level, and Mao just followed Stalin. None of them deserve any praise, each step only deepened the disaster.
It was Engels who first built a kind of cult around Marx, and through his writings particularly in Anti-Dühring, he laid the groundwork for what would later be called "dialectical materialism." As J.A. Jordan rightly observes, Engels conflated three strands of thought: Marx's naturalism (which is essentially a rejection of Hegel's idealism, Feuerbach's materialism, and both French and British materialism and positivism), French positivism, and the so-called laws of Hegelian dialectics.
Engels is correct in pointing out that Marx did not arrive at his critique of capitalism by assuming that Hegel's dialectical laws are somehow embedded in nature, history, or the process of investigation. Rather, Marx first analysed the real workings of capitalism and only then used Hegelian terminology to express some aspects of that analysis. Engels however somewhat misunderstood this. He mistakenly believed that because Marx used Hegelian categories to describe his findings, the Hegelian laws themselves universally apply to all processes of analysis and investigation. This led him to concoct those infamous three laws: the law of the unity and conflict of opposites, the law of the passage of quantitative changes into qualitative changes, and the law of the negation of the negation.
In the preface to Anti-Dühring, Engels even goes so far as to suggest that natural scientists would do well to employ Hegelian logic in order to better grasp their own disciplines, an absurd proposition, ofc. Plekhanov, who can be seen as a precursor to Lenin, picked up on these ideas and developed them further. Kautsky followed suit. Lenin adopted this framework wholesale and deepened it, and it seems it was Plekhanov and Lenin who began calling this bundle of ideas "dialectical materialism."
The problem with Lenin's version is that both he and Plekhanov completely sidelined Marx's naturalism, which, tbf, Engels at least recognised and instead leaned heavily on Hegelian formalism, mixed with a crude version of French positivism and a variety of representative realism like Engels. The result is a kind of mechanical materialism and naive realism that owes more to the mechanical mat
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