Board Thread:General Discussion/@comment-28431168-20160617130858/@comment-27637436-20161106051855

It's unkown, but still a possibility

Gaster looks like a skeleton, the cracked skull kinda gives it away. He speaks in Wingdings (which for the uneducated folk, is a font.). He is connected to science, and Papyrus during one of his calls, tells the protagonist (not spoiling it.) that Sans has a connection with science (Reading science books.). When you're at the core, and call Papyrus, he says "THE CORE! YOU'RE GETTING CLOSE, HUH?, ..." and with the 3 dots at the end, he makes a sad face, if you try to call him again, It's the same 3 dots and sad face, we all know Gaster fell into the core. And of course, the best bit of evidence in my opinion, Sans's skull-shaped blaster in the Genocide battle is called the "Gaster Blaster".

That's all the evidence we have as of now, and Toby's slowly updating the game, adding hints to anything about Gaster, so many we'll eventually find out who and what Gaster truly is.