Warning: potentially major spoilers for Rogue One: A Star Wars Story are ahead! If you don't want to learn which big character from the Original Trilogy might appear, click on another one of our fine articles.
Even though Rogue One: A Star Wars Story will primarily follow a group of new characters, there will be some familiar faces from previous Star Wars tales dropping in. Darth Vader will be looming over Orson Krennic's shoulder, Mon Mothma will be seen as one of the Rebellions' primary leaders, and Bail Organa will appear in a similar position. Those folks provide enough connective threads between Rogue One and previous Star Wars movies, but now it's rumored that Princess Leia Organa will show up as well.
A Reddit user called tphilb claims to have gotten ahold of the Rogue One end credits at their job, and they were able to jot down many of the names listed. One of the names that immediately popped out was Princess Leia, who is apparently being played by Ingvild Deila. Since this was only a list of names, there aren't any details provided about her exact role. Delia's biggest credit listed on IMDB is playing a "World Hub Tech" in Avengers: Age of Ultron, though she has acted in a number of shorts. One would imagine that her role in Rogue One would be a cameo given everything that's already packed into the story.
While this information is obviously in no way official and remains to be verified, it wouldn't be unprecedented for Leia Organa to appear in the movie. After all, A New Hope began with Leia giving the Death Star plans to R2-D2 and sending him on his way before being captured by Darth Vader's Imperial forces. There could be a scene near the end of Rogue One where a Rebel, like her adoptive father, could pass on the plans to her that the main characters had just retrieved at great sacrifice. Such a scene would make it even clearer that Rogue One takes place right before the events of the first Star Wars movie released nearly 40 years ago.
Along with Princess Leia, this Reddit list also named a few other classic Star Wars characters who could appear in Rogue One. Guy Henry is listed as playing Governor Tarkin, a character who has long been rumored to appear in the spinoff and who was integral to the creation of the Death Star. Anthony Daniels is also supposedly reprising everyone's favorite golden protocol droid, C-3PO (R2-D2 was not mentioned), while Game of Thrones actor Ian McElhinney is listed as playing General Dodonna, the man who walked the Rebel pilots through the strategy to destroy the Death Star in A New Hope. Assuming this list is correct, then Rogue One will feel like a good old fashioned homecoming week more than it already does.
Rogue One: A Star Wars Story will be released in theaters on December 16.