She was there at the beginning…. they just didn’t know it. Introduced in X-Men #132 (1980) by Chris Claremont and John Byrne, Teresia was a young girl that had to survive in various war zone countries. In Afghanistan, she encountered and saved a young Xavier, who had just lost the use of his legs. Once he was healed up, he rewarded her by taking her to the US with him. While he trained the original X-men as the face of his mission, he trained her as his personal spy in the Hellfire Club, taking the name Tessa and becoming Sebastian Shaw’s personal assistant. She aided Shaw’s raise in power in the Hellfire Club and feed the information to Xavier. While as a member, she also aided Shaw in a wager with Elias Bogan, which Bogan eventually swore revenge. She would be presence for the Dark Phoenix saga and convinced Betsy, a member of STRIKE at the time, to give up on trying to spy on the Inner Club.

After years of working as a spy, she revealed that truth to the X-men and joined their ranks as Sage. When Rogue discovered one of Destiny’s diary, Storm would take a few of the X-men including Sage to search for the rest of the volumes. While a member of the X-treme X-men, she encounter Shaw and Bogan again. Following House of M, Sage would join the new Excalibur and when that team encountered the Exiles, she would join that team before joined a Multiversal X-men team. In Krakoa, she became the head of X-force when Beast was forced to step from the position.