The Idoneth Deepkin were created by Teclis to act as successors to the aelven races of the world-that-was. While most aelves are passionate, sensitive and emotional, the Idoneth bear a deep spiritual trauma from their time within the belly of Slaanesh, and shunned Teclis’ teachings – causing him to try to kill them.
The Idoneth Deepkin fled beneath the oceans of the Mortal Realms, drawn there by a deep ancestral link with Mathlann, the old aelven god of the seas. Once there, they made a horrifying discovery – the vast majority of their young were born with withering feeble souls. It appeared the race was on the brink of extinction until the sinister art of soul-theft was discovered – the Idoneth could extend their lives and grant new souls to their young by stealing those of other sentient creatures.