According to karl marx, what is the source of capitalist profits?

The Surplus Value

Karl Marx is known as a philosopher but is best known as a revolutionary.

Surplus Value is known as Karl Marx theory (Marxist theory) that clarifies that it is the source of profits which capitalists put to their own use. It the value of a worker's labor power It is also known as the left over when an employer has repaid the cost of hiring the worker