Gaster is the biological father of both Sans and Papyrus, and is the husband of River Person. Once the former Head Royal Scientist, Gaster was always ambitious to discover something new. He has a very intense passion for science and anything remotely close to it. He has always had an interest in studying souls, much like his son Sans does in the present. Gaster has always been clear when showing emotions, and can sometimes get very giddy when excited for something. Gaster has a very high level of intelligence, yet comes close compared to Sans. Gaster is very affectionate towards his family, and is very loving to his wife. He had been good friends with the Royal Family for a very long time, and at one point was supposed to be Asriel's godfather. Gaster is a fan of horror! He enjoys watching spooky movies past midnight and scaring the living shit out of his closest friends for shits and giggles! His weapon of choice is a Scythe! Gaster is incredibly dangerous when wielding it, as his cleverness gives him an advantage on the battlefield. He's fast with his scythe, and can create fissures by slamming it into the ground. alongside his scythe, Gaster is also a master Magic user, able to use all sorts of tricks to get the drop on his opponents! Out of himself, Sans, and Papyrus, Gaster is actually the Second Strongest.. who's the first?

Gaster's disappearance has never been explained...

[I'm not gonna sugarcoat it. My headcannon for Gaster is the way Youtuber Vade handles him. Gaster in this AU has a smooth yet menacing tone to him, seemingly emotionless but makes it clear when he feels upset or angry. He has a somewhat cold attitude but does have his dorky days]