>>713830627
Ghaster in undertale is a scientist who met a terrible fate after a fateful experiment. There's basically no details about him in that game, and what little you can find is well hidden.

Ghaster in Deltarune is identifiable by his peculiar way of speaking and welcomes you when you boot up the game by guiding you through making a "vessel". Though the vessel is discarded by an unknown character, Ghaster still shows up on title screens, game over screens, ect, and generally seems to be encouraging of what we're doing in the game.