The Outsider

Before the Mai-ben'Mach
The Outsider has been repeatedly referenced as having not only been alive during the near-apocalyptic event, but also was a participant in the final conflicts. Whether this is what led him to venture into the Void or it was his punishment is unknown. Curiously, there are no mentions of The Outsider in any remaining records from before the Mai-Ben'Mach

After the Mai-ben'Mach
All that remains important to him is his loyalty to the original royal crown of Arendelle. Of which, none of its remaining bloodline are treated as royalty. He currently is a silent supporter of the Chevaliers, supplying them with his best assassin. However, in return, he has demanded that the rightful heir to the throne be recognized and given at least some portion of Arendelle. Given the current state of the Chevaliers, it's unclear if he will remain a loyal ally.

The Outsider remains primarily in The Void, having not been seen outside of it in quite some time. However his legend remains strong. Some have described him as an angel, others speak of him like a devil. All that can be truly said is that The Outsider has always taken an interest in odd people and circumstances. While often with a specific self-interest in mind, he is rumored to give strange powers to those who please him.

The closest anyone has come to recording him is a single painting of him, stored in the attic of the royal palace. It was reportedly painted by one of the staff when they had a chance encounter with him, claiming they saw him kneeling in front of the throne, before vanishing with a smirk and courtly bow.