The character’s name is Xulivan, on Proudmoore. I can’t seem to find any quests that lead down into Torghast to unlock him.
You must complete the Deep Within, Ashes of the Tower, and The Final Pieces quests to unlock the Runecarver in Shadowlands.
- Deep Within requires you to simply talk to the Runecarver.
- To complete Ashes of the Tower, you must collect 1,250 Soul Ash in Torghast.
- To finish The Final Pieces, you must acquire a Runecarver Memory, an Armor Rune Vessel suitable to your class, and 2 different Missives.
- Reawakening (Optional Quest) requires you to go to the Maw, kill a creature and recover a Runecarver’s memory. The quest is not mandatory and if you collect a memory from elsewhere, you will be able to start crafting and upgrading Legendary Armor just by completing The Final Pieces.
It looks like you completed Deep Within today, and are currently working on A Grave Chance. So you’re on the right track - just keep going 
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