Sacha is one of the 13 Champions of Rajaat, named: Curse of the Kobolds.
When the other champions rebelled against Rajaat, Sacha and Wyan stayed loyal. After Incarcerating Rajaat they were both present when Borys transformed into a dragon. The process destroyed their bodies, but their heads lived on.
Kalak collected them and used them to infuse his templars with spells. Kalak had never undergone the process of becoming a Champion (false) and he convinced Sacha and Wyan to lend his templars their spells.
Later on they would advice and teach Tithian in the way and dragon magic.