Sagat originally appeared in Street Fighter as the non-playable final boss. His next appearance after that was as an antagonist in Street Fighter II, where he teamed up with the criminal organization Shadaloo, headed up by M. Bison.
He wasn't actually playable until Street Fighter II: Champion Edition, but since then, he has made several more appearances as part of the fighting roster in games like Street Fighter Alpha 3 and Super Street Fighter IV, as well as the DLC for Street Fighter V.
The team behind Street Fighter Origins: Akuma is working on this novel, including the writer Chris Sarracini, the artist Joe Ng, and the colourist Esped Grundetjern. It explores his origins before Street Fighter as an ordinary person growing up in Thailand, trying to find his place in the world (likely using his fists).
It should be noted that in the past Sagat has been portrayed in other Street Fighter comics. This includes the Udon-published Chun-Li miniseries Street Fighter Legends: Chun Li, where he played the main antagonist.