Deep dwarf that we met in Oceanscar at the soiree that was being thrown by Lady Eltun Cordon.
It is from him that we learn about dwarves and their interesting properties that require them to wear specialized suits in the upper world. They are not meant to leave the deep caverns. In the past they made a deal with the fey that cursed them with the inability to ever return to the surface without the specialized armor they’ve built. We also learn that the dwarves refer to the surface world as overburn.
The term for a dwarf going “feral” and falling to their surface instability is derro. There is no way to reverse this once it happens.
This information is collected in the page on Dwarves.