The dictatorship of the proletariat originally, in Marx’s work, did not mean a literal dictatorship, but a democratic government run for the workers with the effective exclusion of other potential power centers. He refers to capitalist democracy in turn as a dictatorship of the bourgeoisie, for reference.

Marxist-Leninists are the big offenders here, because two of the major ‘innovations’ to Marxism introduced by Marxist-Leninists (at least, two which are relevant here) are that of the revolutionary vanguard (that you need to give power to a small number of people who are really well-read on theory, and THAT’S what will save the revolution), and the idea that you can ‘skip’ over capitalist democracy and go straight to socialism if you just try really hard and shoot a lot of people who think wrong.

Marx was long-dead by the time Marxism-Leninism came about.