Source is the world energy of Rivellon, from which magic is born. Originally harnessed by the Eternals, the precursor race to the seven races: dwarves, elves, imps, lizards, humans, orcs and wizards. When the Seven Gods rose against their eternal brethren, Source was released into the wider world as part of this release embedded into the seven races the God's created.
The benefits and dangers have swayed the perception of Source over the aeons, in Anno Rivellonis Source allowed Sourcerers to ascend to the height of power in society. Braccus Rex is one such notable ruler who became twisted during his rule. Actions such as his lead to the creation of the Order of the Source Hunters by the Council of Seven to remove him from power. Following his removal this order remained, seeking out and eliminating Sourcerers.
Age of the Damned
Following the acceptance of Ruganol's aid by Dylan Ferol, humans learnt how to wield Source to heal others, allowing them to turn the tide against the demonic legions.
Age of Chaos
Until the Age of Chaos, Source had be used to benefit society. Shortly before Lucian's rise to the mantle of the Divine in 1218 AD, Source became tainted and the healers of Aleroth were no longer able to wield its power for good. Despite Lucian's efforts to discover the reason for the taint, Source never returned to its former prominence as a force for good; instead it became feared.
Following the staged death of Lucian, the Divine Order intensified its hunt for Sourcerers. In part fueled by the acts of Sourcerers like Windego and in part due to the appearance of the voidwoken whenever Source magic was used Sourcerers as a whole were herded like cattle collared and sent to Fort Joy, located on Reapers' Eye under the guise of protecting the wider society.
This change in stance towards Sourcerers caused divisions within the Divine Order. The Order of the Source Hunters, now known as the Seekers, with the assistance of Malady aided in the escape of six of the Sourcerers trapped on the island, of which each of them were appointed by the god of their race as their Godwoken, those who are set on the path to become the next Divine.
From landing on Reaper's Coast and travelling to Arx via the Nameless Isle, the Godwoken gained both the historic knowledge and power of Source. Following their battle with Lucian, Source was finally laid to rest, removed from the world.