When you're reading a fic in a large universe (like Marvel, DCU or Star Trek), and you run into a canon character you're not familiar with, you...
Keep reading and hope the context of the fic is all you need.
Stop and look up that character on wiki or some fandom resource.
keep reading but plan to look up the character later.
decide the story is getting too complicated and stop reading.
ask the author about the character in a comment.
do something else, that you'll talk about in comments.
It depends on how important the character is to the story.
It depends if the story is an AU.
When reading a fic with a large cast, would you find an appendix with a dramatis personæ useful?
It depends if it's an AU.
It depends on how many characters are in play.
It depends on if the characters are pulled from disparate parts of canon.
I've got to figure out how the climax is going to work, in a techo-magical-logistical sort of way, but I think all my plot threads are starting to tie in.
Still got to write the actual racing scene. Still looking for recs of books that have horse racing and/or bareback riding from the POV of the jockey/rider. I've already read a fair bit of Francis, Farley and Henry.