Real communism doesn't need a single leader to maintain control or tonact altruistically. Real communism doesn't have a single leader at all. Resources and control are shared by the citizenry, decentralized to the community, thus the name. I'm by no means an expert on the ideal workings of a national scale communist control structure, but the point would be to form a stateless nation without any bourgeoisie in control anymore, but rather everyone would be of the proletariat and the proletariat would share control.

But you have hit the nail on the head of the problem with the transition to communism that I was alluding to. Normally it requires a populist party to overthrow or fundamentally reform a national system of governance. They take total control of the government and then total control of the nation's resources, factories, properties... the "means of production"... from the bourgeoisie. That part has happened several times in history. It is the rest of the transition that has failed to occur every time. What is meant to happen next is that they then relinquish those means of production back to the proletariat, set up the means of self-governance, and then dissolve themselves and the central government. That has never happened.

The problem is that, once the nation falls under the control of one party, it does require the leader(s) of that party to act, as you said, with pure altruism and willingly give up absolute power. And typically people that become party leaders are the kind of people that seek power and that do not like others having control. The problem is that the process as described requires people that are driven and insentivized to lead a major national reform. And then it needs those same people to act against their own nature and self-interest for ideology and the greater good. This is why that power had never been decentralized in any real world example of a transition to communism. That is what is meant when we say that there has never been a real communist country. There has never been one without a single party/dictator is control. There has never been a decentralized control of resources and power on a national scale. Those things have only ever been achieved on a community level to this date, and those communities struggle as they still must function under and within a capitalist system.