Drego featured heavily in the Mistwalkers campaign, as he became the mentor of Dax' Athla. He was present for many of their adventures, helping them to save the world on multiple occasions.
Drego Sarhain is a Knight-Diligent of the Order of the Gilded Labyrinth, and a diplomat for the nation of Thrane. He's one of the church's few Silver Pyromancers, an arcane spellcaster who channels the power of the Silver Flame. He was trained by Lady Gennara ir'Damilek, with whom he had a somewhat adversarial relationship.
He is Chantalyn Sarhain's cousin, and the two grew up together. They remain close in their adulthood, but their respective duties rarely have them in the same place. They keep in touch with "letters".
His mother is a seamstress, an art that she taught him, and so he is often better dressed than one might expect from a priest. He often adorns his clothing with animated silver flames, giving the impression that he is on fire.
He is also an agent of the Argentum, specialising in the acquisition of magical artifacts and gathering intelligence, but this is not public knowledge.
To see some fiction centering Drego, see Actor, Tailor, Soldier, Spy