Are/were there any SFF professionals (writers, or movie people) who posted on this site?
By professional, I mean someone who did a paid job involved with producing SFF content.
We've also had a few professional comics contributors come through, thanks to one of the employees' ties to this site, right? I feel like I've seen an answer about She-Hulk from someone "famous".
EDITED TO ADD:
The artist for Image Comics' "Chew," Rob Guillory, answered a question about the series: Why are all the USDA agents in Chew women with exaggerated physical features?
The writer for DC Comics/Vertigo's "iZombie," Chris Roberson, answered this question about the series: Has the over- and undersoul theory been used to explain monsters before?
We answered a She-Hulk question for Marvel Comics writer Fred Van Lente, who then Tweeted the question and answer out to his followers: Can She-Hulk's hair be cut?
A question on our site was answered by "Hulk" writer Jeff Parker via Twitter: How does The Incredible Hulk change mass?
While there's no proof of identity, I'm aware of at least one (Danny Rubin posted an answer to How long was Bill Murray's character (Phil Davis) supposed to be in a time loop in the film "Groundhog Day"? )
We can probably count @TangoOversway, who stated that he wrote scripts to be submitted to Star Trek (they were not used, but that's less relevant to me).
He may not have directly asked/answered questions on his own canon, but he is an active professional on this site.
Recently, user SQB asked the question: Who are the architects of the buildings on which these fictional buildings were based? to which Thaddeus replied:
I approve those answers...
I wanted an answer that addressed the fact that we sometimes get professionals involved with our answers, without the professional specifically creating an account here to answer the questions themselves.
In this case, a professional (celebrity handler) was contacted via Twitter to answer a question, and they responded.
Here, the professional artist that created the cover art was contacted by the user, which resulted in not only a confirmation that it was the correct artist, but said artist's website was updated to include the art in question.
To answer this question, Jack emailed the voice artist who voiced the character in question, Snarl.
This is another case of Twitter connecting us to professionals, and phantom42 contacted one of the writers of the show. Their response essentially confirmed all the downvotes on the question.
Peter Beagle responded to an email about DVD royalties for a movie for which he wrote the screenplay.
Two authors got involved in this story-identification question. R. L. Stine replied in twitter to confirm that this wasn't his story; then the writer of the story, Greg Cox, replied when Kyle Hale found the answer.
Carrot used Twitter to reach out to James Gunn, the movie's director, who came up with an answer.
While these don't exactly fit the bill of professional participation, they are participating by proxy (whether they realize it's for our stack or not). These interactions are different than general quotes from professional's Twitter accounts or websites. For instance, JK Rowling's tweets are often cited to answer Harry Potter questions, but those tweets were not given in a direct response to a SciFi.SE member's inquiry.
The following question:
Not only is this an answer from someone professionally involved in the case, it's also an incredibly detailed and thorough answer in its own right, if you take into account the scope of the linked resources, including a Google Drive link containing hundreds of PDFs comprising all filings in the case, which is regularly updated by Sai themselves.
The co-author of the book The World of Ice and Fire and renown A Song of Ice and Fire 'superfan' and collaborator with George R. R. Martin, has made a couple of appearances on this site.
Our first professional author sighting was, to my knowledge, Mark Jeffrey, in response to Tony Meyer's question about differences in the two versions of Max Quick: The Pocket and the Pendant.
Assuming we focus purely on questions answered by word-of-god authorities where that question was prompted by a question asked on SFF:SE, then there are plenty to choose from.
Question About Fantasy Novels By F.J. Hale/Robert E. Vardeman - Robert E. Vardeman
Do they have surnames in Stonewylde? - Kit Berry
What exactly *were* the Klingon gods? - Keith R. A. DeCandido
How can Tristran believe this about his adopted mother? - Neil Gaiman
Is there a Star Trek audio book read by Brent Spiner? - Brent Spiner
Who's the child and her mother that can "talk to flowers" in Ruins? - Terese Nielsen
Why exactly do the Twin Towers still stand in the Kermit-less world? - Kirk R. Thatcher
Why does Watney’s notebook in The Martian have four holes? - Noel Cowell / Neil Floyd
ST:Titan Sword of Damocles ending - Christopher L. Bennett, David Mack
Are there any more Elminster novels coming? - Ed Greenwood
Do I need to read City of the Damned before Kinslayer? - David Guymer
Which order to read the 4 Old Republic novels? - Paul S. Kent, Sean Williams, Drew Karpyshyn
Whose buttocks are these? - Charles Stross
Why doesn't GLOPP mutate humans? - George Broussard
Is Dharia a matriarchy? - Susan Kaye Quinn
Why is Paris flooded in Edge Of Tomorrow? - Chris McQuarrie
Is there a heaven in the Top Cow Universe? - Ron Marz
In The Clone Wars movie, why can't Anakin understand Huttese? - Karen Traviss
Why is the planet Lola Sayu so damaged? - Leland Chee
When and where are the Daggers and Steele books set? - Alex P. Berg
Where did the gold in Fort Knox go? - Patrick E. McLean
Patrick Nielsen Hayden (one of SF's foremost editors, which he won several Hugos for, working for Tor; also a blogger on Making Light with his wife and others) came by. Unfortunately, he didn't stick around.
That's the only name I remember that I recognized from before, but I know we've had a couple of authors pop by (other answers here cite some of them).
There is another answer from an author to a question about (or at least related to) her own work:
John Rennie emailed David Brin and got an answer for this question: Houseflies use humanity to colonize the galaxy
It seems that Madeleine Robins answered a question on one of her books here:
Chuck Jones apparently answered a question about a model that he designed for a Half-Life character:
The person who created the Toby the Targ stuffed animal prop answered a question about whether they're available anymore, at Does a stuffed 'Toby the Targ' toy exist?.
Matthew Hughes also answered a question about a short story of his. After a bit of confusion where his answer was deleted for not answering the question, it was all sorted out and his answer currently resides at Does it have to be those two spells, or would any combination of "impossible" spells work?
Our good friend Edlothiad had e-mailed Andy Weir, the author of The Martian, for an answer on The Martian – what happened to all the video log recordings?
I myself had done the same thing for my comment on The members of Ares 1,2 and 4 (or 5) crews?