Marshal McLuhan (1911-1980) is, I think it fair to say, a once mega-famous but now almost-forgotten 1960s intellectual - the first major analyst of 'the media'.
If you want to know about him, I would recommend a 1968 Penguin anthology called McLuhan: Hot & Cool edited by GE Stearn. This was published at the height of McLuhan mania, when it still seemed possible that he was a 'genius' thinker of the stature of Marx, Weber and Freud (Marx? Freud? - Who they?...)
Yet there were also other voices pointing out that, by ordinary empirical standards of validity, most of what McLuhan said - on a sentence by sentence basis - was just plain wrong!
My evaluation (having read a lot of and about McL on-and-off for more than twenty years) is that he was indeed more wrong than right, and certainly was not a genius (even before his creativity was obliterated by major brain surgery); but he had One Big Idea that was both new and true.
That was the idea encapsulated in his slogan The medium is the message - and it is the insight that the social importance of communications media (such as the lecture, the handwritten book, the printed book, the telegraph, telephone, television, internet) is not exhausted by their content.
The form and nature and properties of the medium is also very important; and perhaps more important than the specific content of the medium, since content may cancel-out in its effects, and also because communicable content is significantly constrained by the medium.
So that, over the long term, the societal importance of the printed book, the telephone or television may have more to do with the special qualities of that medium of communication than with what people write, say or watch.
(Because I think this insight is correct, I am recurrently troubled about the effect of blogging; and engage in a probably futile fight against the nature of the medium by such negative self-limitations as not indexing my posts, not having a blogroll and - nearly always - not cross linking with the day's news and the current blogosphere. By such frictions I hope, somehow, to retain the reader's awareness of the medium, and his alertness to its distortions - not take it for granted.)
McLuhan's One Big Idea seems to me to be both valid and sufficiently counter-intuitive to count as a very significant intellectual contribution.
And for this, if for not much else, McLuhan certainly deserves to be remembered.