The article, report and book classes of (and their class option files) all derive from a single source file, classes.dtx; its contents are extracted to the class files themselves in the course of installing LaTeX.

Of course, since classes.dtx is a documented source file, it may be formatted, for (perhaps) more relaxed reading. A formatted version exists in the base and latex-tds zip files of the distribution.

The author is The LaTeX Team. The package is Copyright © 1993-2006 The LaTeX3 Project.