W. D. Gaster

Joethebro64's Headcanon
"**Please do not edit without permission**"WD Gaster was the Underground's famous Royal Scientist, prior to Dr. Alphys. WD Gaster was a very smart man, he had created the CORE, as well as making a working time machine. WD Gaster was well known throughout the underground, and he had many followers. One day, WD Gaster accidentally fell into the CORE. His body was spread across time and space, and everyone's memories of him were erased. WD Gaster now remains trapped in an interdimensional void located in the Waterfall. His time machine remains broken and unrepaired in his shed, which is located behind Sans' and Papyrus' house. WD Gaster's current appearance is that of a skeleton, with two gaping cracks in his skull, floating hands, and a black cloak. Three of WD Gaster's followers still remain in Hotland, in a split dimension, however. The followers can be summoned if one knows the cryptic message to call out to them.

Rx2 & Shadow Amethyst (AKA Faw)
Since Gaster is unable to speak normally, he uses his hands to communicate. Sans was also Gaster's assistant, which explains the machines that Sans has.

DarkGojiranGhidorah743
Gaster is Sans and Papyrus 's Father, Sans is also his assistant, when Gaster fell into his creation and shattered across time and space, Only Sans remembered him, in order to keep people from being confused, Sans kept this to himself, the followers don't count, since they count as ghosts too. This also explains why Sans has those machines, like Rx2 and Shadow's Headcannons

Howsadd's Headcanon.
Please Do Not Edit Without Howsadd's Permisson. On 16/01/2016 A User On /r/Undertale. Reported that a strane STEAM Account by the name of W.D Gaster In WIng Dings. Opening the Link WIll Bring You To The Steam Account Which is now down mysteriously. Although it is reported that three people managed to add it. Some of which are on this wiki. Once added a few users had conversations with the acccount telling various backstories and information. A Screenshot WAS Taken Of The Profile. The Source Imgur Link has been removed. But Someone Screen-Capped The Image.

The Translation of one of the conversations has been lost. But the Original Wing Ding's Version still Persists; Here.

It is possible to add the steam account by visiting the link.