The Writer, also known as Grant Morrison, among numerous other names, is quite simply the writer of DC Comics and Vertigo, as manifested in the fictional reality.
Believed to be the entity which drew DC Comics on the blank page that is the Overmonitor, The Writer is DC's true supreme being. To him or her, reality and it's inhabitants are just stories characters that can be shaped into whatever he desires them to be, and should he or she become unsatisfied with the current state of creation, it can all be easily altered through a retcon.
Being completely beyond all stories and hierarchies within DC, The Writer is all-powerful and completely unknowable from the perspectives of his or her characters. Likewise, no character can comprehend the complete Writer, instead of only being capable of interacting with representations. Thus while multiple writers of of differing ages, genders, and tastes may manifest in DC to interact with and affect their creations, they are all only aspects of a collective Writer responsible for all stories.
Powers and Stats
Name: Variable. Represents all the writers of DC Comics
Origin: DC Comics
Powers and Abilities: Questionable Omnipotence
Attack Potency: True Infinity (Wrote DC Comics in its entirety, and is transcendent over all of its characters and concepts, as they are all nothing but fiction from his or her perspective.)
Lifting Strength: Irrelevant
Striking Strength: True Infinity
Durability: True Infinity
Standard Equipment: Writing tools such as a computer, a typewriter, pencils, and paper
The reasoning behind this character's rating is this: Grant Morrison has stated in interviews that DC Comics was drawn on The Overmonitor against its will, by a an entirely separate entity. The Overmonitor itself, in fact, is meant to be a representation of the blank page on which the comic is drawn.
Furthermore, Grant Morrison's Final Crisis and Multiversity hold a cosmology built around the duality between Reality and Fiction. There, it is shown that one universe's reality is another's fiction, and characters will often encounter and read their own comic books when traversing between the Multiverse. Likewise, the race of the Monitors are treated as the writers and editors of the entire Multiverse, but even them, alongside the totality of existence are but a microscopic inkblot on white canvas that is The Void.
Coupling all of this information with Grant Morrison's own Animal Man run, wherein the titular character encounters his writer, and learns that he is nothing but fiction, it becomes clear that, despite our general strong reservations for Reality - Fiction Interaction, The Writer is heavily intertwined with, and impossible to separate from DC Comics' fictional mythology. However, this profile should be taken as an exception, rather than a rule, regarding the convention.