Nietzsche is known for his provocative concepts like the 'Übermensch' (Overman), the 'will to power,' and the declaration that 'God is dead.' His poetic and aphoristic style, seen in Thus Spoke Zarathustra and Beyond Good and Evil, profoundly influenced existentialism, postmodernism, and psychology. Though his later years were marked by mental illness, his critique of traditional values and his emphasis on individual creativity remain central to modern philosophical debate.