Richard Dedekind

Although the book is assuredly based on Dirichlet's lectures, and although Dedekind himself referred to the book throughout his life as Dirichlet's, the book itself was entirely written by Dedekind, for the most part after Dirichlet's death.

There is an of the secondary literature on Dedekind. Also consult Stillwell's "Introduction" to Dedekind (1996).