Knuth

In order to typeset his series of books on computing in a fashion similar to the quality of his writing, Knuth invented TeX. One of the secondary reasons to make TeX was cost; typesetting math was very expensive.

In order to be able to push costs further back, Knuth designed fonts. In order to design fonts he invented Metafont.

In order to write large software programs intertwined with documentation, Knuth invented Literate Programming.

And why was he doing all this? He wanted to record everything he knew about programming computers, he wanted to share this in a affordable way, he wanted to address a big audience.