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 without him 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 worst of humanity and the horrific results of his actions. 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.

"Dad Beat Dad"
After making a rubber duck with the ability to breath fire he receives a call from Charlie, making him both nervous and overjoyed. She asked him if he could arrange her to meet heaven's higher-ups but he promptly refuses, then is invited to the Hotel.

Once he arrived he is introduced to the staff and residents, but gets in an argument with Alastor before being interrupted by Mimzy.

When the loan sharks pursuing Mimzy attack the Hotel, he pointed out the chaotic nature of sinners to his daughter. She lamented that Lucifer doesn't believe in her an explains himself in a song. He finally agrees to arrange a meeting with Heaven's higher-ups.

"The Show Must Go On"
He attacked Adam before the latter could seriously injure or kill Charlie. He apologized to his daughter for being late and comically threatened Adam by saying that he was going to "fuck you" instead of "fuck you up", much to everyone's dismay. He proceeded to toy with and berate the angel. Angered that Adam destroyed the Hotel and that he tried to attack him and Charlie from behind, Lucifer unleashed his full demonic form and mercilessly beat up the angel, and then Charlie stopped him, saying that Adam had enough.

After Adam's death, he ordered Lute to take the exorcists and go back to heaven, and then asked the hotel gang if they wanted pancakes. Impressed by Charlie's achievements, he promised to help her in her future endeavors, starting by helping rebuild the Hotel.