A Capitalist is defined as a person who makes the majority of their income from the ownership of assets and capital. For example, a capitalist may receive dividends from shares or rent from property that he owns.
In a sense a person with a private pension can be said to be gaining income from assets they have built up. But, most people use the term capitalist to refer to someone who makes a good living from the ownership of assets.
The term capitalist is sometimes used pejoratively implying that the person makes income without having to work or earn it. Marxist theory stated that a Communist revolution would occur as the proletariat would be disgusted with the Capitalist class who make a living from their work.
Others argue that capitalists are essential for the development of a modern economy. A capitalist will invest in new businesses because of the reward of gaining more money.