Karl Marx (1818-1883) German philosopher, sociologist, economic historian, journalist, and revolutionary socialist who developed the socio-political theory of Marxism (with Friedrich Engels). This was explained in The Communist Manifesto (1848).
Galileo Galilei (1564-1642) physicist, mathematician, astronomer, and philosopher.
Forced to repent before the Inquisition in 1633 because of his new ideas. One of the first times we see the clash between the church and science.