Marleth

 was the grand prelon of the Excrothians. The Unon forbade the time travel the Excrothians were developing and destroyed Excroth with an entropy engine. The Excrothians escaped, but their bodies wizened and they put themselves inside walking tanks, renaming themselves the Lect. Marleth telepathically showed the Ninth Doctor his people's history, and using the Doctor's TARDIS to get there, turned the entropy engine on itself. Marleth and the Unon leader Arnora subsequently destroyed one another. (COMIC: Weapons of Past Destruction)