Lucifer Morningstar/History

Past
Prior to the creation of the Earth, Lucifer was an angel, said to be a dreamer with fantastical ideas for all creation, but the elders of Heaven saw him as a troublemaker who posed a threat to the order of their world. He watched as the angels began to expand the universe and the creation of Adam and Lilith. After Lilith left Adam, Lucifer met her in the Garden of Eden and the two dreamers fell in love with each other. Lucifer, with Lilith, wanting to share the power of free will, offered Adam's second wife, Eve, the Fruit of Knowledge, with this act evil made its way into the Earth which subsequently created Hell. As punishment, both Lucifer and Lilith were sent to Hell, where Lucifer could only see the cruel and the wicked that came from humanity. Ashamed, Lucifer lost his will to dream.

In Hell, now a fallen angel, Lucifer became the ruler of all Hell on the basis of his angelic power, ruling over all the Demons that reside there. At an unknown point, Lucifer became part of an order of powerful demons called the Seven Deadly Sins, each member embodying a sin, with his being Pride.

At some point, he married Lilith, and later fathered a daughter named Charlie Morningstar with his wife. At another point, Lilith left Lucifer for unknown reasons, which sent Lucifer into a deep depression and isolated himself from his kingdom and daughter as a means to cope. The reclusive Lucifer now spends his time in his home coping by crafting rubber ducks, mostly inactive ruling over Hell.

At some point, he started a successful theme park called Lu Lu World that proved to be quite popular with the denizens of Hell. Another of the Sins, Mammon, created a rip-off of his theme park called Loo Loo Land, claiming to be a friend of Lucifer.

Hazbin Hotel pilot
In the pilot's opening song, shadowy figures resembling him appear.

During Charlie's fireworks display after the Extermination, Carmilla Carmine, Zestial and Zeezi are seen watching from a window along with a red-eyed silhouetted figure of Lucifer.

He is later mentioned in Charlie's voicemail to Lilith.

Several photos of him can be seen throughout the Happy Hotel, most notably a family portrait that catches Alastor's attention.

"Overture"
Charlie receives a phone call from her father informing her that the leader of the Angel Army wants to meet and asked if she could go to the meeting in his stead.

"Show must go on"
He attacked Adam before the later could seriously injure or kill Charlie. He apologized to his daughter for being late and comically threatens Adam by saying "I'm gonna fuck you" instead of "I'm gonna fuck you-up" much to everyone's dismay. He proceeded to toy with and berate the angel. Angered that Adam destroyed the hotel and tried to attack him and Charlie from behind, he unleashed his full demonic form and mercilessly beat-up the angel. Charlie stops him before he could kill Adam and walks away. After Adam's death he ordered Lute to call-off the extermination, and proposed the troupe if they wanted pancakes. Impressed by Charlie's achievements, he promises to help her in her future endeavors by starting by helping rebuilding the hotel.