Charles Sanders Peirce
American Philosopher and the founder of pragmatism. His contributions to philosophy and related subjects are immense, ranging from logic, mathamtics, scientific methodology, probability and induction, theory of signs, and epistemology in general.
However, since he was not accepted by his contemporary academic world, his later philosophy became esoteric and sometimes romantic. For instance, take his rhetorical statement "man is a sign". Peirce regarded his theory of signs (called semiotics) as basic to his (later) philosophy, such statements as this seem very important, but it is often hard to make its sense, and there may be wide possibilities for its interpretation. Here, let me briefly mention Prof. Burks's clear-cut rendering in terms of the concepts of computer science: Man is an adaptive algorithm. Try this out!
Notice that Peirce means by "man" the psychical aspect of man's life, which is nothing but a train of thought, and thought is a sign; moreover, Peirce regards man's body (organism) as merely an instrument of thought; you may here notice an obvious analogy with Richard Dawkins's "gene-vehicle" distinction.