Tessa was a spy for Professor Xavier who infiltrated the HFC. Later she became a full fledged X-Man named Sage.
I love & envy her memorization skills, poise and intellect.
There are so many inspirational stories featuring this wonderful, indomitable character. Anticipation builds to a fever pitch as we finally have a fresh new place for us to share them all.
Getting aquainted with Sage:
http://www.comicvine.com/sage/4005-4559/
Fan Origin by George Gozum:
http://www.rainernyc.com/tessa/t1.html
We can even discuss Diana Fox here.