Kevin Clamely was the CEO of Horzine, and they were tasked with a secret research project by the British government to create a "super soldier."
Dr. Clamely at some point decided to attempt to use the research in order to clone his deceased son. This lead to the creation of the first Clot. Dr. Clamely could not bring his son back, but perhaps his new children could be the "super soldiers" he was tasked with creating.
New variants were created in the underground facility in London, as well as spreading the research to other facilities throughout Western Europe.
In the Wyre Forest, not far from Wales, a secret facility working on biological camouflage created the Stalker, though it is not known whose DNA the female specimen are based off of (but it is speculated to be Kevin Clamely's daughter, Rachel).
It is currently unknown when or how a Nazi scientist named Hans Volter got involved. However, given the extensive laboratory set up in Volter Manor and the nature of his research, he and Horzine may go back many years if not decades.
For more information, see: The Outbreak
As one would expect with such dangerous experiments, eventually they got out. The exact way remains unclear in the aftermath of the devastation. Maybe the powerful Fleshpound simply could not be contained, or maybe a group of activists investigating Horzine accidentally released all the specimen, or maybe Dr. Clamely released them himself, as his mind had already long-since turned towards using his "children" to take over the world.
Regardless, the outbreak began in London and soon spread across Europe, and possibly the entire world. Humans fought back when and where they could, with Survivors banding together to face off against the waves of creatures, arming themselves with whatever they could find or trade for.
As the military closed in on Kevin Clamely, he had his remaining loyal scientists use the products of their research to transform him into the Patriarch, so that he could survive and lead his children to victory.
Battles broke out all over England as the Patriarch used all of his secret facilities to their fullest.
Eventually he was cornered in a facility deep below the subway station, but he escapes on the train to Paris, leaving behind two clones of himself for his attackers to face. Fortunately they were aided by a timely appearance by Rachel Clamely and were able to pursue the Patriarch to Paris.
Dr. Hans Volter had already begun militarizing the specimen in France, and oversaw the experiments for a time while the Patriarch upgraded himself.
Horzine, after having ousted Dr. Clamely from his position as CEO, was now interested in taking back their property and helping humanity to survive the monsters they'd allowed to be released. To this extent, they offered jobs to any remaining survivors to be paid mercenaries in helping to clear out the specimen. The idea was that anyone who had managed to survive this long might as well get paid to keep doing it. However, some suspect Horzine may still harbor some shadier motivations. Perhaps pitting the mercenaries against the Zeds is an experiment in and of itself?
And the Patriarch's experiments also continue...