It's useful to distinguish between the "ruling class" and the "governing class" (or power elite) in order to clarify this.
The power of the capitalist ruling class is _structural_. The structure of capitalist society gives some people -- those with sufficient money -- the power that allows them to use M to make M' (money to make more money), even if they aren't directly involved in exploitation. Further, the whole society has to please these people (within limits) just to keep accumulation going, to provide jobs, human subsistence, etc. (unless we're organized enough to replace these folks).
On the other hand, the power of the governing class is _instrumental_. They are in charge of the state apparatus and are organized in the government. Their individual personalities can affect the specifics of the historical process (though not always as they please, since they are constrained by capital's laws of motion, etc.) via the decisions that they make.
Typically, there's a big overlap between the ruling class and the governing elite (with the latter being smaller than the former). Sometimes, however, especially during socioeconomic crises, the actual capitalists are not in government at all but are totally replaced by professional politicians, military officers, etc. -- Jim Devine / "There can be no real individual freedom in the presence of economic insecurity." -- Chester Bowles