This resolves when Deltarune Chapter 7 releases, unless it comes out after Jan 1 2035, in which case it will resolve N/A.
If it's not fairly clear in the game I will also resolve N/A.
Related questions
Surprised nobody added an "He is his own character" option yet
Updated on this after seeing the argument that you name the vessel, and so they likely share a similar metanarrative role to Chara, and thus probably play a significant role in the plot
if it ends up being something like "gaster, who did things via possessing the vessel" then sorry for making this hard to resolve
@Ibozz91 Personally, I find it weird that:
A) Papyrus is absent from the plot so far, despite being a major character from UT.
B) Papyrus’ absence is commented on often.
There are several explanations for this, but I think these hint towards Papyrus being the Knight.