The Debrune were a humanoid (Vulcanoid) species that had left Vulcan centuries before as part of an exodus from the world. Evidence of their society is found on abandoned outposts from the time of their journey.
To the interstellar community the Debrune are an ancient civilisation of Vulcanoid travellers hypothesised to have left the planet to find a new homeworld after a 'calamity' on the world.
Their own history tells of a group of exiles from a 'greater Fleet' breaking away under the leadership of an Admiral Debrune (from whom they take their name) and carving out a successful warp capable nation spanning over a large stretch of the starscape 'east' of Vulcan. The Debrune have tranformed their early history into myth via a heroic narrative concerning the life of the leader Debrune. They appear to have had some level of contact with the Romulans before the collapse of their Empire. The reason for the disappearance of the Debrune from the Alpha Quadrant is connected to the Portal.