Both Robespierre and Marx had been well-born and well-educated but rather spoiled and, as young adults, found that they had no particular talent or inclination to pay their own way in life through gainful employment. Consequently, they shared a hatred for those who succeeded economically through their own efforts and sought a governmental system that would drain such people of their achievements, to be shared amongst those who had achieved less.
Interestingly, neither one saw himself as a mere equal to the proletariat that they championed. Each saw himself in the role of the one who was to cut up the spoils and make the decisions for the rest of society.
It's worthy of note that collectivist leaders never see themselves as becoming the humble and patient recipients of whatever bones the government chooses to throw them. They always see themselves in the role of rulers.