Board Thread:Wiki Discussion/@comment-43347532-20190731192237/@comment-26907577-20190731193431

We don't know. My guesses: - Breaking the barrier/keeping his job - Certainly an adult, but likely irrelevant as most other characters' ages are beyond "school-age" and "since the war". - The CORE, and possibly some sort of machine to navigate the barrier using timeline stuff (which possibly is in Sans' basement and was involved in creating Deltarune)

The last of those is the most flimsy. He's a secret character who only appears by chance and is mysterious by design.