From what the Internet says: He was born in the USA. He graduated from Arizona State University. In 1993 (or 2003?) he started developing his own operating system, that became TempleOS in 2013. During that, he lived in his parents' house and programmed TempleOS day to day. According to him, he created TempleOS following the specific instructions given to him from God, who wished him to build the Third Temple. TempleOS was updated for the last time in 2018. Terry Davis often called himself "the smartest programmer that has ever lived".
TempleOS is free and public domain.