Board Thread:Fun and Games/@comment-25958552-20160730164841/@comment-26887879-20160828135226

Well, we don't know if Gaster is a skeleton or not. But there is a hint that he might be a skeleton, his message in unique font, Wingdings. Sans and Papyrus are only other characters who speak in different font and they're both skeletons.

Even his name W.D. Gaster hints he might be named after font. W.D. for Wingdings and the name Gaster is very simmilar to Aster which is also a font.

And that drawing  added in a recent patch heavily leans towards "Gaster is Skelebro's father theory" in my opinion. Sans and Gaster obviously have some sort of connection. However, there still isn't enough evidence to prove what exactly it was...