Sage, also known as Tessa, is a fictional character in the Marvel Comics universe. She has most often been associated with the X-Men and the Hellfire Club, whom she spied upon for Professor Charles Xavier.
A mutant, Sage possesses a number of mental abilities and was originally presented as the personal assistant to the Hellfire Club’s Sebastian Shaw, but an extended retcon revealed that she had been one of the first mutants discovered by Professor Xavier. She has been a member of the original X-Men teams, the X-Treme X-Men, Excalibur, the Exiles, and a cross-dimensional X-Men team similar to the Exiles known as the X-Treme X-Men.