[Software] Phrase or saying? NO

... or all of them?

[Chalky] A sin or seven? NO

[GL] A fictional person? On this occasion I'll be generous and allow you the two questions in one - YES and NO
[Chalky] GTA V? NO

[Chalky] Fictional animal? YES *some applause*

[Software] Mermaid? NO
[GL] Skippy? NO
[Raak] Named individual fictional animal? YES *a little more applause*

[Dujon] A.A.Milne? NO
[CdM] In more than one of: book. film, TV, radio, grand opera? YES

[Lovely Gravy] Disney? NO

Nobody has checked this yet.

[Software] Actually, I did.

[Software] Human? NO (yes to fictional animal, no to fictional person, hence not a person. You are correct that nobody asked that question directly though)
[GL] Dog? YES *more applause*
[Dujon] Male creator? YES

[Lovely G] Connection with the Simpsons? YES, but not an important connection, IMHO.

[Software] Greyfriar's Bobby? NO
[Dujon] First appearance in print? YES
[GL] First appearance on TV? NO (see above)

[Ye Olde Softeware] Lassie? NO

[Dujon] In a children's story? NO

Ooops, not sure what happened there, but I thought I'd add a summary, just to help out, as I thought this would be simple. Not that there's much to summarize.
This is a fictional dog; created by a man; has appeared in multiple media (from the list: book, film, tv, radio, Grand Opera), but first appeared in print; has a slight link to The Simpsons (which is unlikely to be useful).
The AOTC was not created by A.A.Milne; is not a Disney character; is neither Greyfriars Bobby nor Lassie; was not introduced in a children's story.

[GL] HotB? NO