In the 1978 series Battlestar Galactica, Lucifer is a new type of Cylon designed to aid Count Baltar in hunting down humanity. Created even before the slaughter of the Twelve Colonies, Lucifer makes his first appearance in the second episode, "Lost Planet of the Gods".
Lucifer was much more humanoid than the Cylon Centurions, with eyes, smile, and nose. He also had a conical head, full of lights that moved around as he thought. You never saw his body or arms, as he was clad entirely in a thick, stiff robe of sparkly red material and kept his arms crossed in front of him. Lucifer is an IL-series Cylon, created as an administrator for human-occupied territory. We're told that the IL-series Cylons have two (two!) brains.
Lucifer was portrayed by Felix Silla, and voiced by Jonatha Harris (from Lost in Space).
Lucifer ended every audience with Baltar with an unctuous, "By your command" -- which became the series' catch-phrase.