Xanti was a clone of Uriel. He was created as part of the Final Chapter's plan to take over Gallifrey and turn it into a military power. However, when Uriel saw the newborn Xanti, the first of the clones, he abandoned the Chapter. He hid Xanti in a Chapterhouse and went into exile to conceal the truth.
However, Luther eventually discovered who Xanti really was and kidnapped him. A living link to the Eye of Harmony, Luther installed Xanti in a TARDIS, which he planned to take back to Gallifrey's origins and change history, fulfilling the Final Chapter's original goal. The Eighth Doctor managed to prevent this, but in the process Luther killed Xanti. (COMIC: The Final Chapter)