Aside from dirk's suggestion, these are the common options most bloggers choose from.
(1) You can choose a theme that provides for and displays individual authors. There are theme reviews that can assist you in determining if a theme provides this "authors" feature. Look in the section titled "Display post author".
(2) If the theme you prefer to use does not this feature then you can create a category called "Authors" as a "parent" category and then create "children" (Tom, Dick, Harry) sub-categories for each author's name under the parent category Authors.
(3) Or if neither of the above options are suitable then you can have each author include a byline in the posts they create (i.e. ozrisk's suggestion).