Erin Xingmay
From BHH Wiki
Erin Xingmay, sometimes spelt Erin Xiangmay, was a spymaster, an alchemist, and in later sources, the first Helundtu, one of the Four Great Mages. Erin was Robert's key character in the Suijing Cycle. The least developed of Robert's characters, Erin had little backstory before the late 560s, by which time he was known at court as a powerful private spymaster who was also (reasonably) loyal to the king. King Jonathan I made him the Helundtu, a Great Mage responsible for potions, healing and alchemy, in 571.
In summer 2017, Erin was supposed to have been a Child of the Moon, though this concept had been abandoned by that November.