Murmur is your advisor throughout most of Hellgate London. Players first encounter him at the start of the game, at Russel Square. He helps players by giving them information and advice if needed. He will start most of the primary quests and he is the end to most of them. He follows you to almost every station and directing to towards a goal. He is also accessible through the quest log for advice.
After killing Sydonai and the final cutscene starts Murmur appears trotting happily with his torso ripped out and jaw missing.
Murmur tells players that the player has ruined eons of work, meaning that Murmur was working with the demons for the whole time. He is pleased that the player has killed Sydonai, because he can now control the army of demons. Murmur is the Great Duke and Earl of Hell. After Murmur finishes talking with the player, he sends them back into the portal.
He brings a book possibly out of a different dimension or by summoning it. After which he then says "The First will not be happy about this." as The First is the almighty Demon of Hell.