During 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 Greel had the doll-like but homicidal cyborg known as the Peking Homunculus assassinate its commissioner, an event which nearly precipitated a sixth World War.
He considered himself a driving force in the project in which his nation pioneered time travel. Apart from that he also personally experimented with the catalytic extraction chamber, an attempt to cannibalize life energies. 100,000 "enemies of the state" would be 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". A Human monster, Greel would think nothing of unprovoked murder and cannibalism.
After the defeat of the Supreme Alliance in the Battle of Reykjavik, Greel used a time travel process utilizing a time cabinet to travel back in time to the 19th century China with the Peking Homunculus. Greel passed himself off as a god, Weng-Chiang, to a lackey, Li H'sen Chang, and, with Chang posing as a conjurer and the Homunculus as Mr Sin, a ventriloquist's dummy, 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 for him so that he might use their life energy to restore himself, a method which was inherently flawed and only accelerated the damage. Eventually he tried to restore his body using the time cabinet, but was instead shoved inside his own extraction chamber by the Doctor, resulting in fatal cellular collapse.