|Out of universe information|
He ruled over the people for centuries, but was eventually overthrown in what came to be known as the "War of the Gods". It is not known whether or not this was the Volsinii rebelling against their "god" or a System Lord choosing to make war on Karun, though the latter has more evidence to suggest it.
Karun's legacy would live on, however, as the people kept the legends of their "god" alive and indeed even named a toxic gas, Karun's Shroud, after him long after his death. (RPG: "Friends and Foes: Stargate Season Two")
- Karun on Wikipedia