Sabbath Dei

Sabbath was an enemy of the Eighth Doctor.

Biography
Sabbath was born in 1740.. He studied at Cambridge and worked for the Secret Service before defecting in 1780.

Sabbath encountered "Leviathan" under the River Thames as part of his indoctrination ceremony into the Service. He set up his own power base independent of the Service. After leaving the Service, Sabbath sent a message via a number of corpses of the Service's "ratcatchers" saying "leave me alone, and I'll leave you alone".

The Eighth Doctor chose Sabbath for his best man at his wedding to Scarlette. Sabbath later removed the Doctor's second heart to allow himself to travel through time in the Jonah. (EDA:The Adventuress of Henrietta Street)

Sabbath had agents which were to him the same as companions were to the Doctor. Among them were: Juliette Vierge (EDA:The Adventuress of Henrietta Street); Sasha and Jueves; (EDA: History 101) Jaxa and Roja, former Time Agents; (EDA: Trading Futures) and The Angel Maker (aka Elizabeth Kelly). (EDA: Camera Obscura)

Sabbath arranged for the Doctor and the Clock People to meet on a Plutocratic Empire colony planet. (EDA: Anachrophobia)

While near death, Sabbath met Death and returned the Doctor's second heart to him. (EDA: Camera Obscura)

Sabbath later assisted Fitz Kreiner, Anji Kapoor and the Doctor when multiple realities began to converge and mix. (EDA: The Last Resort) Sabbath was finally killed after turning his back on his employers and helping the Doctor. (EDA: Sometime Never...)

Alternate Versions
A Sabbath existed in at least one alternate timeline where he apparently knew the Doctor by reputation (but not by face). (EDA: The Domino Effect)

In the timeline where the "War in Heaven" was still being waged, Sabbath became a member of Faction Paradox, rather than an agent of beings attempting to replace the Time Lords. He was used as an agent of the Great Houses to hunt Justine. His personality was similar to his in the main timeline. (BBV: Movers)

In a timeline where the War in Heaven had ended, Sabbath still worked for the Secret Service. (FP: Political Animals)

Personality
Sabbath was generally opposed to chaos and believed that unauthorised time travel created parallel universes which threatened reality. Sabbath was confident in his mental abilities. Aided by the Doctor's second heart, he survived a journey into Death's realms. (EDA: Camera Obscura)

He was incredibly stubborn and disliked beings who lorded their powers over others, including the Doctor.

Habits and quirks
Sabbath used many pseudonyms, often variations upon his chosen name of Sabbath. (EDA: Time Zero) Although he openly scorned his agents, he was fiercely loyal to them. (EDA: The Adventuress of Henrietta Street)

Appearance
Sabbath was bulky and muscular. His body was getting fat. He kept his head almost shaved. This was not a political statement or an attempt to intimidate people, but to save time and energy in grooming. (EDA: The Adventuress of Henrietta Street) Many of Sabbath's clothing choices echoed the Doctor's, for example, he wore a linen suit after adopting the role of Time's Champion. (EDA: Camera Obscura)