When the Alliance fell to the Filipino Army in the Battle of Reykjavik, he became a wanted war criminal but escaped by using an experimental time cabinet. Greel went to the late 19th century China and then to London, where he continued his depraved activities on a smaller scale.
In Greel's time, the Earth was split into a number of warring alliances. The Icelandic Alliance and Greel's Supreme Alliance were at war. The Icelandic Alliance fell when, at Greel's command, the doll-like Peking Homunculus assassinated its commissioner Ingrid Bjarnsdottir, (TV: The Talons of Weng-Chiang; AUDIO: The Butcher of Brisbane) setting off World War VI. (PROSE: Doctor Who and the Talons of Weng-Chiang)
In the early years of his dictatorship, he was visited in his bunker in Reykjavik by Romana, who landed there by accident while trying to update the Doctor's TARDIS. She gave Greel the idea of time travel and gave him the business card of a plastic surgeon in 1998. Mishearing her, he thought she said "1890s". (PROSE: Under Reykjavik) Greel considered himself a driving force in his nation's time travel project.
He also personally experimented with the catalytic extraction chamber in an attempt to cannibalise life energies. One hundred thousand "enemies of the state" were massacred for these experiments.
As the Supreme Alliance's ironically-named Minister of Justice, Greel carried out an atrocity earning him the title of the "Butcher of Brisbane." (TV: The Talons of Weng-Chiang) A human monster, Greel thought nothing of unprovoked murder and cannibalism. (PROSE: Under Reykjavik)
After the defeat of the Supreme Alliance in the Battle of Reykjavik, Greel utilised a time cabinet to travel with one Peking Homunculus back in time to 19th century China. Using information provided by his fifth incarnation, the earlier Doctor was able to prevent further bloodshed, bringing the brief Sixth World War to a close. (TV: The Talons of Weng-Chiang; AUDIO: The Butcher of Brisbane)
Living as a god
Greel passed himself off as the god Weng-Chiang to Li H'sen Chang. With Chang posing as a conjurer and the Homunculus as a ventriloquist's dummy called Mr Sin, they eventually found themselves in London.
The passage through time had caused great damage to Greel's DNA, deforming him. He wore a mask and concealing clothes to hide his true form. While Greel lived in fear of Time Agents, Chang abducted young women, including Emma Buller, for Greel to use their life energy to restore himself via his catalytic extraction chamber, a method which was inherently flawed and only accelerated the damage being caused to his body; the Doctor dismissed it as nothing but "an advanced form of cannibalism" that only saved Greel having "to chew the grisly bits".
Eventually he tried to restore his body using the time cabinet, but was instead shoved inside his own extraction chamber by the Fourth Doctor, resulting in fatal cellular collapse as the chamber extracted everything he was already running low on from his own body. (TV: The Talons of Weng-Chiang) The Fifth Doctor would later note that Greel's supposed death here was a part of the Web of Time. (AUDIO: The Butcher of Brisbane)
Even almost forty years after his death, the Tong of the Black Scorpion still venerated Greel as a god, while Chang's daughter Hsien-Ko- essentially immortal but also sterile due to her father's exposure to zygma energy before her conception- sought to divert the time cabinet to 1937 by generating a massive amount of Piezoelectricity to disrupt the zygma beam while it was en route to 1872. She intended to use this opportunity to torture Greel for the dishonour he had caused her father, trapping him in a new version of the extraction chamber that would trap Greel in an isolated cavern where he would be sustained by small animals, but the Doctor prevented this plan by destroying Hsien-Ko's nuclear power generator and then using the TARDIS as part of a near-time ram to force the cabinet back on course. (PROSE: The Shadow of Weng-Chiang)
Survival in the 20th century
Greel's mind was later reconstituted by Guinevere Godiva in 1968 by using a Venusian crystal. He took possession of Detective Inspector Dave Sacker to continue living. Jago and Litefoot discovered Greel's plan to return. Greel died when Ellie Higson stood in the distillation chamber and overloaded the power of his time cabinet. (AUDIO: The Final Act)
Behind the scenes
Weng-Chiang was originally going to be the Master, following on from The Deadly Assassin, but producer Philip Hinchcliffe had this changed as he didn't want to have the Master revealed as the secret villain again. Alan Barnes has pointed out several clues in the story that still point to the original plan: the "time cabinet" and Greel referring to Leela as "the first morsel to feed my regeneration". (DWM 475)