The Sorcerer is technically your character, Stirling, as the first time he appears in the story (through mention) is in TRH, Act 1. However, practically he is a character that I nurtured into what he is now, starting with mentioning how a Sorcerer (that could be more than one person) cursed Ankoria, in the map description. I'm not sure if there were any in-between appearances until A History Lesson, but this is the one story where he appeared for the first time. Before that, during SA planning I often shared my opinions on the Sorcerer. I think that the three Sorcerers (the ones who cursed Ankoria and the one who banned technology or whatever) were officially announced to be the same for the first time in the Timeline.