Karl Marx
Marx was socialist.
Karl Marx.
Karl Marx invented Radical Socialism.
It’s not clear that anyone ‘invented’ Socialism.
Karl Marx
The answer is Karl Marx.
Socialism/Communism
Karl Marx created the ideology of Marxism, which is a socio-political theory that focuses on the idea of class struggle and the eventual establishment of a classless society. He is also known for co-writing "The Communist Manifesto" with Friedrich Engels.
Karl Marx had a view of a true socialist society which he termed scientific socialism.
KARL MARX had the view that history was inexorably trending to communism and that capitalism would improve to socialism and socialism would improve to communism.
Marx made a detailed analysis and critique of capitalism, and advocated its replacement by a classless Socialist society.