Cauldron-Born are undead Jaffa created by placing a dead body into a specially-modified Sarcophagus called the Black Cauldron. Instead of healing the body and raising the dead, it animates it as a Cauldron-Born. The Cauldron-Born know instinctively who their creator is and obey him.
Cauldron-Born make excellent shock-troops: they're silent, they follow every order given, they have no fear, feel no pain, and fight on until they are (mercifully) killed again. They are easily replaced by the dead of their enemies, the ultimate Jaffa recycling program. One drawback though was Cauldron-Born couldn't speak.
The Cauldron-Born made up the majority of any ground force Manannan mac Lir sent into battle. They were first deployed by Arawn during the uprising against Balor. (RPG: "Living Gods: Stargate System Lords")