|Out of universe information|
Prior 3 is a Prior who appeared in Stargate: The Ark of Truth.
He commanded an Ori Warship, tracking the Odyssey from Celestis. When they caught the ship, he fired upon it. He was affected by the Ark of Truth when it was activated and amplified through the Doci's crystal and into all of the Prior staffs. ("Stargate: The Ark of Truth" )