Donald Knuth has written what are arguably the most beautiful books with the TeX system.
Now I understand that Knuth wrote them in plain TeX, and still uses plain TeX for his current projects. Which, to me at least, raises the question: how is it even possible to write a book of any significant size without the benefit of the LaTeX macros and the CTAN packages, some of which, I believe, will only work with LaTeX?
For instance, how did he do his drawings? How did he define his environments? (Did he?) How did he manage floats?