This should be Kreiner or Kreiner (Interference - Book One), per T:HONOUR.
Talk about it here.
For more detailed information see the Fitz Kreiner article. Father Kreiner was the original Fitz Kreiner, who merged with Remote technology and the Faction Paradox biodata-virus and became an enhanced human over time as a result. He left Anathema and became a full member of Faction Paradox; he also became the oldest living member of the Remote after leaving the Faction.
During his time with the Remote, Fitz hunted and killed many renegade Time Lords, including the Rani and the Master. One or more of these kills may have been of clones. (PROSE: Interference - Book One)
Father Kreiner tried to follow the Doctor by grabbing onto I.M. Foreman's Travelling Show when it assumed the form of the TARDIS, believing it to be the Eighth Doctor's ship, but was flung into the Time Vortex. He was plucked out by I.M. Foreman and trapped in her bottle universe's Time Vortex. (PROSE: Interference - Book Two)
Father Kreiner was at least a thousand years old when viewed on a Time-Space Visualiser on Gallifrey. He was retrieved from the vortex and re-encountered the Eighth Doctor and the "new" Fitz, initially regarding Fitz as a mere copy of himself. Father Keiner briefly tried to help his old friend after the Doctor convinced him he genuinely regretted abandoning Fitz; he had only done so because he was convinced that Fitz was dead. Grandfather Paradox shot and killed him for his betrayal, leaving the other Fitz as the only surviving version of Fitz Kreiner. (PROSE: The Ancestor Cell)