Who is Professor Marshall McLuhan from Travels in Hyper Reality: Essays and what is their importance?

In the book Marshall McLuhan is a professor that has written a book called "Understanding Media". The focus of the book, similar to Sedlmayr's, is that man has lost his center. His argument states that all of the technological advancements of man should be seen as media which affect our "sensibility". In effect, he is saying that the medium has become the message.