The bald Scotsman is in fact an established DC Comics character called The Writer, who was created by Grant Morrison. The Writer — whose real name is also Grant Morrison — first appeared on-panel in Animal Man #25*, where they revealed to the titular hero that they were the mastermind behind all of the terrible things that had happened to him and his family. Not because The Writer was a cruel and horrible supervillain bent on world domination or anything — no, The Writer was simply doing their job, using their superpowered narrative-crafting abilities to manipulate Animal Man's life for the entertainment of comic book readers in our reality.
The Writer had another cameo in Suicide Squad #58, in which they are recruited onto the infamous team of supervillains…only to be brutally killed moments into their first mission.
To recap: the Grant Morrison of our reality created a fictional Grant Morrison who exists in DC Comics continuity, and either one or both of those Grant Morrisons are also canonical characters within the DC Cinematic Universe. Which means that it is both legally and artistically possible that DC could make a Grant Morrison solo spin-off movie or TV show in which they team up with various incarnations of Batman and Superman and Flash and whoever else. Assuming this happens, the script will likely be written by Geoff Johns, who will undoubtedly force Grant Morrison the fictional superhero to face off in a magical duel of the wits with their natural archnemesis, The Original Writer.
*I also own an autographed copy of Animal Man #25, but now I'm starting to wonder: was it signed by Grant Morrison, or by the character of The Writer from the comic books, or by the cinematic adaptation of The Writer?
