Board Thread:General Discussion/@comment-28974149-20180305043309/@comment-32182236-20180324171707

"Another thing to note is that while we know what Gaster was, we do not know his personality or who he was."

He was a mad scientist. And considering his relation to Sans and Papyrus, he's almost certainly Mysteryman.

"Though, it seems he completely lost it when he wrote Entry Number Seventeen and we know he must enjoy science..."

Hence him being a mad scientist.

"I wonder if he enjoys Puzzles too considering he designed to CORE to be a little maze that can be changed every day to create a new challenge...."

It was created to stop humans. Like any other puzzles.

"We also know he was super famous, Great even, after all he invented the CORE and had dedicated followers..."

His brilliance was irreplacable. That's why nobody can fix what he made.

"We also know his genius knew no bounds. And that he tried to experiment with DT based universe manipulation, destroying himself in the process leaving behind a melted husk and several other pieces scattered across all Space-Time.  But that's pretty much it. And we know he likes to have input on his experiments from "you two".  Such a juicey mystery."

One of them is almost certainly Sans. We already know Sans worked with Gaster. The other could be Alphys, explaining why she partook in similar experiments.