Time Lord messenger (Genesis of the Daleks)

A Time Lord messenger entasked the Fourth Doctor with preventing the creation of the Daleks. (TV: Genesis of the Daleks)

Various conflicting accounts existed regarding the messenger's identity, with sources indicating he was an incarnation of Deliavatsud, (PROSE: The Dalek Problem) Brastall, (PROSE: A Device of Death) Ferain, (PROSE: Lungbarrow) Valyes, (AUDIO: Ascension) or Jelpax. (PROSE: Divided Loyalties)

Origins
By one account, the messenger was the final incarnation of Deliavatsud, a director of the Celestial Intervention Agency who went rogue in an attempt to subvert the APC Net's predictions of total Dalek domination. (PROSE: The Dalek Problem)

By another account, the messenger was Ferain, a member of the Celestial Intervention Agency. (PROSE: Lungbarrow)

According to one other account, this messenger was Valyes, who was sent in disguise by Narvin after the Daleks invaded Gallifrey. (AUDIO: Ascension)

By yet another account, the leader of the team who identified the Daleks' threat to the universe and developed a plan to stop them was named Jelpax. (PROSE: Divided Loyalties)

Yet another account named this individual was Valentine. (WC: Death Comes to Time)

On Skaro
After a transmat beam used by the Fourth Doctor and his companions was redirected to Skaro, the messenger visited the Doctor.

He explained to the Doctor that the Time Lords had forseen a time through their temporal projections when the Daleks would dominate the universe and gave him a mission to disrupt the Daleks' timeline by preventing their creation, making them less aggressive, or identifying an inherent weakness. He also gave the Doctor a time ring to leave Skaro once the mission was complete. Then he vanished. (TV: Genesis of the Daleks, PROSE: Doctor Who and the Genesis of the Daleks)

Further adventures
Following the failed intervention in Skaro's history, the Time Lord messenger's duties increasingly revolved around the Daleks. He watched as they planned a campaign called Pa Jass-Vortan in retaliation for the Time Lords' actions. When the Daleks used their time corridors to travel to Shoreditch in November 1963, (PROSE: The Slyther of Shoreditch) an event known as the Shoreditch Incident, (PROSE: Who Killed Kennedy, et al.) he travelled there to stop their mechanically augmented Slyther from tracking advanced technology in the region, which he assumed was the Doctor's TARDIS. First, the Time Lord researched the local culture and decided to order a half pint of bitter shandy from a local pub, where he encountered the Seventh Doctor.

The Time Lord explained the situation to the Doctor and agreed to return the Slyther to its home space and time if the Doctor would help him track it. Together, they travelled to the funeral parlour where the Doctor had stored the Hand of Omega and commandeered a black hearse. The Time Lord nervously stayed in the vehicle as the Doctor stole a piece of the undertaker's clothing from his house, then drove the hearse as the Slyther attacked. Struggling and screaming, he drove right through the fence of an electricity substation, leaving a deep bloody gash on his forehead. After the Doctor killed the Slyther, the Time Lord happily left using his Time Ring, disappearing with the creature's corpse after warning the Doctor about Pa Jass-Vortan one more time. (PROSE: The Slyther of Shoreditch)

A man in black who wore a pointed collar was known to a time traveller who (PROSE: Cyber-Hunt) once was a future incarnation of the Doctor. (COMIC: Party Animals) When his home planet was destroyed, the time traveller made a deal with the man in black; he would be removed from the lifecycle (PROSE: Cyber-Hunt) of the Doctor (COMIC: Party Animals) in return for the planet's restoration. Although the traveller's wording once implied they did not share a homeworld, the man in black gave him a mission to hinder the developments of the Cyberon on Carson's Planet, (PROSE: Cyber-Hunt) much like how the Time Lord messenger had greeted the Fourth Doctor on Skaro. (TV: Genesis of the Daleks)

Fate
Deliavatsud was subsequently tried for unauthorised intervention and executed by disintegration. (PROSE: The Dalek Problem)

After the Dalek intervention, Ferain was the Director of Allegiance for the Celestial Intervention Agency and author of An Alternative History of Skaro: The Daleks without Davros. When Ferain arrested Leela, the Seventh Doctor recognised him from the trenches on Skaro. (PROSE: Lungbarrow)

According to one account, the Time Lord messenger who had given the Fourth Doctor his mission opposite the Daleks during the Genesis Incident (TV: Genesis of the Daleks) was known as Saint Valentine. He had a close relationship with another Time Lord who went by Saint Antenor, and they were known, together, as "the Saints".

In a time when Gallifrey had been left in ruins, Valentine and Antenor, collectively known as "the Saints", were part of "the Fraction", the order of surviving Time Lords who watched over the Laws of Time. The two went into voluntary exile on Earth, with Valentine posing as "Doctor Valentine" at a London university while Antenor became "Professor Antenor". The two were murdered by the assassin Nessican, acting on the orders of General Tannis, yet another surviving member of their kind who wished to rule the universe alone. (WC: Death Comes to Time)

Behind the scenes
murdered by Tannis. The character was voiced by Anthony Stewart Head. However, this wiki does not consider Death Comes to Time a valid source.
 * In a deleted scene from the end of Return of the Cybermen, the Time Lord messenger would have appeared in the TARDIS to tell the Fourth Doctor that his failure to succeed in his mission had caused his own history to reoccur in slightly different ways and may lead to a Time War. This was meant to explain the contradictions between Return of the Cybermen and Revenge of the Cybermen, as well as between The Haunting of Villa Diodati and Mary's Story, and Human Nature and Human Nature.