Lucifer

Lucifer is an extremely powerful demon from the Inner Circle, who tried to kill Christopher and Jupiter Constantine, until he was sent back to Hell by John Constantine. He is also responsible for the death of Anne Marie Flynn.

Claiming John and his Children
With Constantine taking his own life as a teenager his soul is condemned to an eternity in hell. After being resurrected John devoted his life to securing his entry into heaven. It is said that Constantine and his children are the three souls Lucifer would come to personally collect.

Trivia

 * "Furcifer" is Latin for "scoundrel." His name was also likely chosen due to its similarity to Lucifer.
 * When Furcifer appears in the guise of John Constantine, he resembles another comicbook character, Demon Constantine, an evil doppelganger created with John Constantine's evil side, Nergal's blood and Alistair Crowley's soul.