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Dr. W.D. Gaster is a posthumous character in Inverted Fate. He was the former Royal Scientist, creator of the CORE and the father of sans and PAPYRUS.



Gaster was a tall, slender skeleton with a perpetual grin and a square jawbone. He wore a suit under a black lab coat, boots and a pair of glasses taped to the temples of his skull.


Reclusive and eccentric, Gaster was as ambitious as he was intelligent. He had a tendency to pause between words while speaking. He was highly secretive, having written all his notes in secret code. He was eerily fascinated with the prospect of a human living amongst monsterkind and had longed to study a human SOUL up close.


Dr. W.D. Gaster served as the Royal Scientist for several decades until his sudden demise thirteen years prior to the events of the main story. 

Prior to Asriel’s birth, Gaster created the CORE; a technological wonder that would provide the Underground with limitless energy for years to come.

Some time after the Integrity SOUL was claimed, the Mage came to Gaster for help in understanding their time-travelling abilities. Over the years, the two studied the secrets of the human SOUL.

In the Mage's final letter to Gaster, they expressed regret that they could not find all the answers he sought and left him with one final lead: their ability to SAVE, RELOAD and RESET was tied to their will just as much as their SOUL. Due to this revelation, Gaster pressured Queen Toriel to give him their SOUL after their passing; a request that she angrily rebuked.

At one point, through unknown scientific means, Gaster created a child whom he named Sans. A decade later, not long before the Mage’s death, he created a second son, Papyrus, in hopes that his children would carry on his legacy after his time had passed.  

Around the time the Mage died, Gaster started greatly focusing on SOULS and a machine that would revolutionize monsterkind by tapping into the powers of a Monster SOUL and rebirth them into something greater and stronger. One day, he was ready for his first field test with Sans with an estimated explosion percentage of 0.0025%. He hopped into the machine and began the experiment, but disaster struck.
The power was overloading, red alerts activating, and the CORE at huge risk of meltdown. Despite the grave danger, Gaster refused to exit the machine, and Sans was left with a decision. Risk the CORE exploding on the small chance the machine works...
... or lose his father for all others to walk away safe. He chose the second option, firing a Gaster Blaster at the machine, preventing the CORE's destruction and the damage it would've caused. This resulted in Gaster falling into the CORE, causing his very being to become shattered into countless fragments that were scattered across space-time. Ultimately, Gaster perished, torn apart by two of his creations as a rsult of his failed final experiemnt.


Following his untimely demise, Sans took his place as Royal Scientist in an attempt to resume his father's work. Alas, the machine could not be repaired. After a year, Sans resigned from his position and moved to Snowdin with Papyrus.

During his time as Royal Scientist, Sans took on Undyne as an apprentice, teaching her everything he knew. A decade later, she would succeed him as Royal Scientist. Meanwhile, through Undyne‘s influence, Papyrus gained an interest in science and became the Royal Scientist's Aide. The blueprints for the machine were later uncovered by Undyne, who took inspiration from the old machine to create one of her own - the DT extractor.

As for the doc himself, some of his fragments are components of the Memoryheads, while others manifest cryptically on occassion, notable ones being the "mysteryman" and "[REDACTED]". His new state allowed him to gain a new level of sentience, essentially being omnipresent. Gaster became aware of the previous timeline and how Asriel Dreemurr inadverently created current one, becoming quite intrigued by it.


  • Concept art of Gaster was released to Patreons prior to the reveal of his design in Part 50.
  • Gaster is aromantic/asexual.


To be added

Main Cast FloweyFriskCharaPAPYRUSAsgore DreemurrNapstablookSansAlphysMad Mew MewMettatonUndyneToriel
Ruins DummyRuins Bullies
Snowdin Dogamy and DogaressaDoggoLesser DogGreater DogSnowdin TrioSnowmanJerryMonster Kid
Waterfall Bassiere von Dohj IIIKnight KnightMadjickRG 01 and RG 02GersonMasaSpout WassarBratty and Catty
Hotland RG 03 and RG 04GlydeSo SorryParsnikAstigmatismMigospelMisyrmMuffetBurgerpants
The CORE Robot 98Robot 100The Season Dudes
True Lab MechamalgamatesMemoryheads
Other Characters Fallen humans (The Mage) • LilacW.D. GasterSpamton