Over the decades, all of those and many more have been listed as sources of inspiration in the various D&D books themselves. Gary Gygax has mentioned Howard’s works as one of his inspirations. (And of course, they served as inspiration to Michael Moorcock, as well.) Fritz Leiber’s (again inspired by Howard) Lankhmar was even turned into a D&D campaign setting.
(Although Leiber can be considered a contemporary of Howard’s rather than follower, he stated in his foreword to “Ill-Met in Lankhmar” that he wanted to create characters who were “closer to human nature” than Conan or Tarzan.)