This is a conceptual historical study of Karl Marx’s worker. The purpose of this study is to examine Karl Marx’s usage of the worker concept, and compare the picture, or pictures, of (the) worker as it is portrayed by Marx with the corresponding usage of the worker concept by the First International. Using the method of conceptual history, I have in texts written by Karl Marx and the First International sought the synchronic as well as the diachronic connotative meaning of the worker concept. In my study, I find that Karl Marx discusses two types of workers; in his earlier, more existential writings the worker is portrayed as an alienated victim, whereas in his later, more political writings the worker possesses an emancipatory potential. I also note how it appears to be Marx’s political worker concept that came to be used by the early workers’ movement, and through that has imprinted our modern, implicitly marxist, understanding of the the worker concept.