The Monk

The Monk, in some accounts called Mortimus, was a former friend of the the young Doctor on Gallifrey and a renegade Time Lord. He was amoral and enjoyed actively meddling with history to his own selfish ends.

Youth
Mortimus was a friend of the Doctor during the latter's first incarnation, when they both attended Academy. They belonged to a cabal of ten rebellious young Gallifreyans known as the Deca. (PDA: Divided Loyalties)

Reunion with the Doctor

 * See the Monk's TARDIS

Mortimus owned a Mark IV TARDIS. (DW: The Time Meddler) According to the Monk, he had left the Doctor's home planet some fifty years after the First Doctor. He delighted in meddling with history, specifically the history of Earth, to change it for his own amusement and for what he thought the better. (DW: The Time Meddler)

He lent mechanical assistance to the builders of Stonehenge and gave Leonardo da Vinci tips on aircraft design. At the time that the First Doctor encountered him, the Monk was trying to prevent the Norman Conquest of 1066 as part of a plan to guide England into an age of technological prosperity. At that time he wore a monk's habit to gain the trust of the locals, hence the name by which he is usually referred.

The Monk was at this time a well-meaning but childish man, not half as clever as he thought he was. He never seemed to realise the seriousness of what he was doing. The Doctor sabotaged the dimensional circuit of Mortimus' TARDIS, making it the same size inside as outside, reducing the interior to dollhouse proportions. (DW: The Time Meddler)

Second Encounter with the Doctor
The Doctor ran into him again on the volcanic planet Tigus. Mortimus sabotaged the lock on The Doctor's TARDIS, though that did not stop him from getting inside. The Doctor stole Mortimus' direction controls to use in his effort to stop the Daleks.

Mortimus' TARDIS landed in ancient Egypt. Knowing of the Daleks, the Monk went along with their plans to avoid being exterminated himself, while trying unsuccessfully to convince the Doctor and his companions of his honourable nature. The Doctor tinkered with the chameleon circuit of Mortimus' TARDIS, making it take various shapes, finally that of a police box. He stole its partially compatible directional unit, leaving Mortimus stranded on a cold, icy planet. (DW: The Daleks' Master Plan)

Ally of the Ice Warriors
Mortimus allied with the Ice Warriors and battled the Fifth Doctor in a complex scheme involving alternative Earths and a giant sonic weapon. Mortimus now preferred his own TARDIS to appear as a police box, did not wear a monk's habit, and referred to himself as the Time Meddler. (DWM: 4-Dimensional Vistas)

Work for the CIA
For a time the Monk worked for the Celestial Intervention Agency. (PDA: The Quantum Archangel) During this period, the Monk was responsible for the Legions' imprisonment. (MA: The Crystal Bucephalus)

The Sleeze Brothers
Some time in the 21st century, the Monk tried to rig elections in what may have been the United States to stop President Sinatra from winning a third term of office. As he began this mission, he landed his TARDIS on a busy freeway. The Sleeze Brothers, El Ape and Deadbeat, collided with it, damaging their vehicle. At the same time, the companion-less Doctor landed his TARDIS in the same area.

Besieged by angry brothers and an irate Doctor, the Monk slipped back into his TARDIS and took off. The Brothers hijacked the Doctor's TARDIS at gunpoint and ordered him to follow the Monk's TARDIS through time. A chase ensued, and the two TARDISes flitted to several famous mysteries in Earth's history. Finally, the Doctor and the Sleeze Brothers made the Monk's TARDIS implode. This apparently caused the creation of the Bermuda Triangle. (DWM: Follow That TARDIS!)

Death's Champion

 * The Monk regenerated at least once. When they next met, the Seventh Doctor did not recognise him by sight.

Mortimus created a series of alternate timelines (NA: Blood Heat, The Dimension Riders, The Left-Handed Hummingbird, Conundrum) in a scheme employing the Chronovore Artemis. Mortimus now used his real name and posed as a 1976 record executive in England. He had also, by this time, served as the Champion of the Eternal Death in the same way that the Seventh Doctor served as Champion of Time, making himself servant to a being much more powerful and intelligent than himself. Mortimus aided the Vardans' scheme to avenge themselves on the Doctor and the Sontarans by conquering Earth, a planet of continued strategic value to the Sontarans and of importance to the Doctor. His plan was undone thanks to the Doctor's companion Ace, who pretended to side with him until she could free Artemis. The vengeful Artemis subsequently took Mortimus away to make him pay for her imprisonment. (NA: No Future)

Mortimus later tried to take Antonio Salieri back in time to kill Mozart when he was still a child. Mortimus was stopped by the Seventh Doctor and the Tramp. Mozart escaped unharmed. (ST: The Tramp's Story)

The Book of Kells
Gaining Lucie Miller as a Companion, the Monk travelled to Ireland in 1006, seeking an artefact known as the Book of Kells. During this time, he once again encountered the Eighth Doctor. (BFA: The Book of Kells)

After an argument with Lucie, the Monk abandoned her on Deimos. He tampered with Ice Warrior history to create a new timeline in which a group of Ice Warriors woke up early and re-terraformed Mars to take it back from the humans. This plan was stopped by the Doctor, who set history on its proper course. The Monk managed to persuade the Doctor's companion, Tamsin Drew, to leave the Doctor and travel with him. The duo set off to find the Daleks' help in defeating the Doctor. (BFA: The Resurrection of Mars)

The Monk helped the Daleks invade Earth as they had in the 22nd century. He used a Dalek virus from the far future and gave Tamsin the job of stealing human artefacts from museums for his personal collection. (BFA: Lucie Miller) After the Daleks destroyed the collection in an attempt to kill the Doctor, he decided to help the Doctor. He saved Susan Campbell and him from the bomb that destroyed the Daleks. He was then ordered to leave the Doctor's sight after the Doctor found out that he had deployed the virus on Earth. (BFA: To the Death)

Behind the scenes

 * The Monk has the distinction of being the first Gallifreyan besides the Doctor and Susan in the series. (In The Daleks' Master Plan, the Daleks seem to refer to the Doctor and the Monk as "humans", though they may simply use the term loosely). The name Time Lord would not appear until The War Games.
 * For some time there was speculation that the Monk was actually an earlier incarnation of the Master or the War Chief, who appeared in The War Games. This is stated as fact in The Doctor Who Role Playing Game, which created its own continuity. However, this theory has been contradicted by the Monk's appearances in novels and comics.
 * It's a mis-statement that this character was ever called "The Time Meddler" or "The Meddling Monk". Both of these "names" are taken from viewer's out-of-universe knowledge of the titles of the overall serial and the second episode. The Doctor comes close to giving the character these names, however, calling him "a time meddler" and "that meddling monk". It's more epithet than name. "The Monk", as a name, derives more from Steven and Vicki's attempt to call him something, at least within the confines of The Time Meddler. By the events of BFA: The Book of Kells, it's clear that the Monk has appropriated the name. By the incarnation that faced the Eighth Doctor, he was doing a Master-like wordplay that indicated he thought of himself as "the Monk". He called himself "Abbot Thelonius" – a sly reference to jazz great Thelonius Monk.