Darwin, Charles
Darwin is not the founder of evolution theory. Before Darwin, there had already been evolution theories since the ancient Greek time. Particularly since the 16th Century with the rise of science, Georges-Louis Leclerc Buffon and Jean-Baptiste Lamarck had developed evolution theory more seriously. Darwin's grandfather, Erasmus Darwin was also an evolution theorist.
The reason why Darwin's evolution differs from the ones that came before him is because he provided an explanation for the 'why', the mechanism of evolution. After encountering Malthus's population theory that our human society is doomed to compete for survival caused by exponentially growing population and therefore food shortage unless we actively control the population growth, Darwin applied the idea of competition for survival to Nature as well and argued that evolution happens by 'natural selection' where the most effective forms of life to their given environment persist to the next generations.
Darwin's theory, though often falsely celebrated for its ground-breaking originality, was nevertheless influential. Herbert Spencer borrowed Darwin's evolution theory based on competition and applied to the society, theorizing 'Social Darwinism' and popularizing the phrase 'survival of the fittest.' Social Darwinism provided legitimacy to racist imperialism.
On the contrary to the right-wing thinker Spencer, Karl Marx also took Darwin's notion of competition and applied to his theory of class struggle.
Between Malthus, Darwin, Spencer, and Marx, they all paid attention to the notion of competition, but what it meant in each their theories are quite different. Malthus seemed disinterested whether competition was men's nature or nature's mechanism or not. He wanted to avoid this miserable state by controlling population growth. For Darwin on the other hand, competition became a more central theme in his theory. Spencer, like Darwin, hinged much upon the notion of competition for his social theory. Marx take on competition was a complete opposite to Spencer. Spencer was on the conservative end and Marx was on the radical end of political spectrum. For Spencer, status quo was the proof of competition, but for Marx, change would be the force of competition. Marx was more future-driven and life-seeking than Spencer.