A professor at University of Toronto, and a major contributor to media theory, Marshall McLuhan is likely most famous for his insightful quote, "The medium is the message."
Though only containing five words, this cryptic quote has changed the way in which media is consumed. There is a lot to understand from this one sentence, and it delves into a deep discussion on the relationship between the content of the media and the forms in which society accesses it. What I think McLuhan was saying is that rather than separating the content of the media from the way we receive it, both these factors are extremely linked, meaning that the medium - television, newspapers, etc. - is actually the message about our society. For example, it isn't necessarily the information on Facebook that says a lot about our generation, but rather the fact that we use Facebook - which tells us how technologically-dependent we are and that we have become much more narcissistic than previous generations. Another example would be that rather than the content of a television show describing our society, which it does do, it is the fact that we watch television overall that will make a change in our society. For example, one might say that television causes more laziness or has killed conversations, which are societal effects or messages that have happened as a result of the television itself, not really what the television was broadcasting. This quote was an extremely important step forward in the study of media and communications and still applies today to show how the media all around us affects our society's behaviours