Thalia

Thalia was a Lord Chancellor in the High Council of Time Lords.

Like all Time Lords, Thalia was taken from her family at the age of eight for the selection process in the Drylands. Staring into the Untempered Schism as part of a Time Lord initiation rite, Thalia was inspired by what she saw in the Schism. (PROSE: A Brief History of Time Lords)

Thalia was one of the High Councillors who sentenced the Fifth Doctor to death to stop Omega from taking over his body. (TV: Arc of Infinity)

Behind the scenes

 * In Doctor Who Magazine 100, which gave a brief history of Gallifrey and the Time Lords, it was reported Thalia was an Arcalian and that Cardinal Zorac and she were sent by Borusa into the Death Zone, where they both perished.
 * Thalia was originally supposed to return in The Five Doctors but Elspet Gray was not available. The character of Flavia was created to fill her role.