Since the identity of the Alternate Spacetime Vegeta, who was introduced very early on in the story, has been a point of curiosity, let the answer be revealed right here.
Like Main World Son Goku, Alternate Spacetime Vegeta is a transmigrator, and the universe from which he originally hailed before his transmigration was none other than the universe where Ashalon defeated both him and Son Goku.
Much like Main World Son Goku, he was reborn driven by a deep sense of lingering resentment. However, the difference is that Main World Son Goku achieved rebirth with the aid of the Heavenly Dao's power of that universe.
Chapter 418