Steven Moffat (in-universe)

Steven Moffat was credited with writing down the afterword to a book of fiction about the Doctor, under dictation from a temporally-displaced Professor Candy who had been stranded in 1996 Birmingham by the Doctor. (PROSE: Afterword)

Parallel timelines
In a meta-fiction universe visited by the Eleventh Doctor where his life existed purely as fiction, a certain Steven was the head writer of Doctor Who.

Behind the scenes
Another in-universe version of showrunner Steven Moffat appeared in The Five(ish) Doctors Reboot, played by the real Moffat. This parodical Moffat was the showrunner of Doctor Who like his real counterpart, but had an exaggerated childish personality, being seen playing with Doctor Who action figures in an overtly childlike manner when he knew no one was looking.