Ludwig Wittgenstein was one of the most important philosophers of the 20th century. Wittgenstein revolutionized philosophy in several ways; unfortunately, Wittgenstein's work is difficult to understand for most people and thus it's difficult for most people to fully appreciate his ideas and his influence.
Chon Tejedor writes in his book Starting with Wittgenstein:
The purpose of [Tractatus], as Wittgenstein saw it, was to reveal the great issues and problems that had dogged philosophers for centuries as being essentially shams: mistakes of understanding which could be dissolved by clarifying the language and the concepts in which they were couched. In carrying out this task of clarification, Wittgenstein saw the Tractatus as effectively signaling the end of traditional philosophy in its entirety. The great centuries-old debates were really just the story of the Emperor's new clothes writ large; the Tractatus would be the lone voice crying out the truth . . . if anyone would ever read it, or understand it.
Just as other people were starting to get to grips with his work, though, Wittgenstein himself was becoming dissatisfied with it and was taking the first steps along a road which would eventually lead to him returning to Cambridge, there to dismantle the logic of the Tractatus entirely.
In its place he would propose an entirely new philosophical method – one that would crystallize in the book Philosophical Investigations (PI). Although this process was already underway when he came back to Cambridge in 1929, Wittgenstein remained, at that point, sufficiently persuaded by his earlier book to present it at his doctoral thesis.
The story of Wittgenstein's personal life as well as intellectual develop also happen to be among the most interesting in recent memory. Chon Tejedor doesn't really get into that, though; except for a bit of information at the beginning, Tejedor is far more concerned with Wittgenstein's ideas than his life. That's not a criticism, but it is something to keep in mind if you're considering this book.