A short history of LaTeX and PDF
LaTeX was written on top of TeX by Leslie Lamport in 1984 and 1985. As Lamport wrote in the preface of his LaTeX manual when comparing LaTeX to its TeX ancestor:
LaTeX adds to TeX a collection of commands that simplify typesetting by letting the user concentrate on the structure of the text rather than on formatting commands. In turning TeX into LaTeX. I have tried to convert a highly-tuned racing car into a comfortable family sedan. The family sedan isn't meant to go as fast as a racing car or be as exciting to drive, but it's comfortable and gets you to the grocery store with no fuss.