How I think Philip Wittebane and his brother's story goes.
Philip and his brother (who I'm gonna call Caleb) were born in the Salem Witch Trials era. They were taught their whole life before the Boiling Isles that witches are evil.
Caleb is presumably Philip's older brother, and he's also good at carving, since he carved a mask for kid Philip. That same mask is what Inner Belos (kid version) is wearing. (Just a little thing I wanted to point out).
They were either lured to the Demon Realm with the flame from a witch's hand or brought there with full consent. Caleb looked entranced by the flame, while Philip looked a bit hesitant, holding onto the mask Caleb carved for him. Either way, they looked like they went into the Demon Realm pretty young.
If they were young when they went into the Demon Realm, that means they grew up there. I'm guessing that if that's the truth, that means that Caleb either slowly forgot about what they were taught and Philip never did, or he never believed in the Salem Witch Trials in the first place.
Caleb falls in love with a witch and gets them pregnant. He introduces his witch partner to his brother, who hides a knife behind his back. Philip thinks Caleb is a traitor for falling in love with a witch. Philip attacks Caleb with the knife (after the introduction?), Caleb pulling out his own and they fight to the death in a ring of fire. Caleb didn't want to kill his own brother, and that's how Philip won.
Caleb's pregnant partner, distraught by his death, attacks Philip with magic as he runs away from the scene; them actually hitting him as he runs away.
Philip either got cursed by that witch's wild magic (this is what caused is hatred for it) or he got cursed earlier. Remember how Eda got out of her curse because King reminded her of who he was? What if it was like that for Philip and Caleb, and that's why he was hugging him in that one picture from Hollow Mind.
Caleb's partner has the same wild, untamed hair as Eda's, and since they were pregnant, I think she was a Clawthorne; meaning Hunter, Belos, Lilith and Eda are maybe related.
Philip hates witches and wild magic. They're most likely the reason he was cursed. And so he grows up trying to find a way to kill all witches. First, he finds a temporary solution to hold back his curse since he no longer has his brother. Second, he finds out a way to get an incredibly loyal sidekick to stand by him as he does all of this. He finds out what grimwalkers are and creates one for himself.
Going back a bit, this is around the era where Lilith and Luz go back in time; also the time where he finds the Collector. The Collector is most likely connected to him (like the way King got connected to the Collector in EOTW) and he said that the Collector is going to help him. Another theory: Maybe Lilith is the reason he hates witches?
So he was already on the journey to finding out how to create a Grimwalker by Elsewhere and Elsewhen. Maybe the Collector told him? I don't know. He creates a Grimwalker (most likely using the lungs from the Stonesleeper Luz and Lilith rode on) and makes it in his brother's image. This time he's loyal.
And then the story goes on like what we saw in Hollow Mind. Belos changes his name, spreads lies, destroys a village, nearly kills all the villagers (who he's using as TEST SUBJECTS for perfecting the sigils) with the sigils, and so on.
The Day of Unity is going to kill every single witch on the Boiling Isles with a sigil, so he's trying to get every single one of them (since leaving someone alive is a bad idea (Caleb's partner is an example)) as seen in Labyrinth Runners. He does this because he'd "do anything to protect humanity from evil". He thinks he's doing the right thing. His moral compass was destroyed the moment he decided to kill his own brother and eat all those palismen. He doesn't know that the Salem Witch Trials are done. (This absolutely isn't me justifying ANYTHING Belos does. He is a horrible person).
And that's that. For now.
Philip and Caleb were born during the Salem Witch Trials. Going into the Boiling Isles, Philip keeps that mentality (that witches are bad) while his brother doesn't. Caleb falls in love with a witch (who is probably a Clawthorne) and Philip considers that treachery and kills him. Caleb's partner attacks and probably curses him as he runs away. Philip hates wild magic and witches because they're the things that got him cursed in the first place and because he grew up during the Salem Witch Trials. The Day of Unity is gonna kill the entire witch race. And here we are.
(Here's all the pictures! Have a good day/night/afternoon!! :D)
