Nergal

Nergal is a powerful demon who was summoned by John Constantine in a botch attempt to defeat another demon possessing Astra Logue, only for Nergal to drag Astra into Hell killing and damning her for all eternity.

Biography
When facing a demon possessing Astra in New Castle, England, John conjured up Nergal from Hell intending to compel him to drag the lesser demon back to Hell and save Astra. Instead Nergal killed Astra violently and dragged her soul to Hell where she was subsequently dammed for eternal suffering. This caused John to suffering immense guilt and often had nightmares of Nergal killing Astra and made it his mission to free Astra from Hell and kill Nergal. Ritchie Simpson, who was present for the event, also frequently endured nightmares and blamed John for Nergal's actions.