Pirate!Gaster is an out!code created by LunarSnowCross. He travels the multiverse by jumping from AU to AU in a ship that he stole from the first AU that he visited. The ship jumps directly to different AUs without stopping in the anti-void. While in other AUs, he pillage it for resources, collects the human souls for the ship, and gathers the Gasters, Papyrus, and Sans to conducts experiments on them so they'll be more "compliant" and "better". When he leaves the AU, it gets destroyed from the force of the jump to another AU.
Pirate comes from a fell AU. While in his AU he was conducting an experiment that dealt with time travel with the human souls and a device. The experiment was successful, but it kicked him out of his AU and damaged him. While he recovered, he was reevaluating his plans of inter-dimensional travel, and how to travel without incurring the damage from the jump. So he came up with the idea of using a vessel instead, and stole a ship after recovering. He took the skeletons of that AU and the human souls, and jumped to another AU after hooking up the device to the ship.
The Gaster, Papyrus, and Sans of the AU that he traveled to weren't really happy that he took them from their home so he thought of the only thing that would keep them compliant with him, and that was to brainwash them by experimenting with them.
While traveling the multiverse, he learned that there is an anti-void because Ink kicked him into it after stopping him from destroying an AU. He, and the other skeletons he gathered, were stuck in the anti-void for a period of time until he met Yin!Aster. She helped him out of the anti-void after he struck a deal with her that whenever she needed him, he will come to her without question. After retaliating and loosing, he agreed to Yin's deal. So it won't happen again, he made contingency plans for any situation where he won't be able to collect humans souls.
Pirate!Gaster is dressed like classic Gaster, but his shirt is red. He has cracks going from the left side of his eye to the back of his skull. On his right side is a mask that covers part of his face where part of his skull is missing.