Ruler of Hell

The Ruler of Hell (informally King or Queen of Hell) is the title and the highest position of authority in Hell held by either the Archangel Lucifer or a demon in his stead.

History
It is unclear who was the first ruler of Hell, though Lucifer - as the creator of the demons - as matter of fact had claim to the throne. It is unknown if he ever got to act as ruler, as he was imprisoned soon after Hell was created.

The first known ruler was Prince of Hell Azazel, who took the mantle after the other Princes chose to abandon their duties. In his role as a Prince of Hell, Azazel was simultaneously the general of Hell's army, which he took command of and ruled with tyranny, yet he was said to be a fair ruler.

Azazel's eventual goal was to free Lucifer from his prison, and to do so he needed to free Lilith and create a Special Child who would kill Lilith as part of the 66 seals binding Lucifer. Azazel achieved both tasks before his death, after which the demons struggled to choose sides between the Special Child, Sam Winchester, and Lilith. Lilith ultimately took control and was the ruler of Hell, as well as the Queen of the Crossroads, until Sam fulfilled his destiny and killed her.

Her death set Lucifer free from his Cage and all the demons flocked to his side. Lucifer ordered the demons to work for the Four Horsemen of the Apocalypse as he set about bringing the end of humanity. His defeat and re-imprisonment at Sam's hands left the throne of Hell vacant. Crowley attempted to hand over the throne to Ramiel, one of the Princes, but he refused, instead suggested to Crowley to take it upon himself to become the new King, which Crowley does.

Crowley met minor opposition from the remaining Lucifer-loyalists led by Meg. Crowley managed to outplay his opposition and ruled as the undisputed King of Hell until Abaddon, a Knight of Hell, resurfaced and challenged him, leading to another civil war in Hell as the demons struggled to choose sides again. After Abaddon's death, Crowley reclaimed the throne and punished all those who chose Abaddon's side. Two years later, Lucifer escaped his Cage a second time and took control over Hell, and later Heaven, while Crowley was kept as a prisoner until he managed to escape captivity.

Following the battle with the Darkness, Lucifer lost interest in both Hell and Heaven, leaving the throne vacant as the demons did not wish to accept Crowley anymore. To regain his former position, Crowley hunted Lucifer down and helped the Winchesters defeat him. Believing Lucifer had been re-imprisoned in his Cage, the demons reluctantly returned to Crowley's side. In reality, Crowley had begun torturing Lucifer in a newly-designed vessel meant to obey Crowley's command. Once Lucifer became submissive, Crowley presented his new "dog" to the demons.

Unfortunately for Crowley, Lucifer was still plotting against him and the demons were aware of this. They pretend to cheer on Crowley's "success" and in Crowley's eyes, he has once again become the undisputed King of Hell. When Lucifer does escape, he presumably kills Crowley and regains control over Hell. Crowley survives, and joins the Winchester brothers in defeating Lucifer once more.

Crowley admits to Sam and Dean that he doesn't like being King anymore. He chooses to commit suicide to ensure Lucifer is trapped in an alternate reality. Crowley's death and Lucifer's imprisonment leave the throne of Hell vacant.

A few days later, the Prince of Hell Asmodeus takes the throne of Hell until Lucifer returns. After finding that Lucifer can't be found, Asmodeus states his intention to give the throne to Lucifer's son Jack with Asmodeus as his adviser. Once a weakened Lucifer returns from the alternate reality, he is confronted by Asmodeus and Lucifer demands that he give up his rule. Seeing his father's poor state, Asmodeus decides to fully take on the role as King and imprisons Lucifer and Castiel as he prepares for the invading Michael.

Characteristics
The ruler of Hell can control the fate of any soul that goes to Hell and has such a high authority that he or she may even trade any number of souls in Hell as per their wish, as seen when Crowley gave Castiel "fifty large," fifty thousand souls from the pit, to make a showing in front of Raphael during the civil war in Heaven.

The King or Queen of Hell can also alter Hell's appearance and how it is run, as Crowley redesigned Hell following Lucifer's reimprisonment and replaced the previous method of extreme physical torture with continuous queuing (which served as a psychological torture for all in Hell). While other demons have ruled Hell previous to them, only Crowley, Abaddon, and Lilith have used this title to describe themselves.

With the exception of Lucifer, a Ruler of Hell must be a powerful demon. Crowley, being a mere Crossroad Demon, was able to maintain the throne after the Winchesters eliminated all the other powerful demons who could challenge him. Since the Princes of Hell were uninterested, three of them were spared.

The demons themselves seem capable of voting who they want to serve. This led both Abaddon and Crowley to use torture to convince a demon to choose their side. As the demons will naturally follow Lucifer, Crowley felt he had to display dominance over the archangel in order to earn loyal from all of his subjects.

In Stuck in the Middle (With You), it is revealed that in the absence of both Lucifer and Lilith, the Princes of Hell are next in line for the throne of Hell.

Known Rulers of Hell

 * Azazel
 * Lilith
 * Lucifer
 * Crowley
 * Abaddon
 * Asmodeus

Trivia

 * Upon Hell's creation and before Azazel, it is unknown who was the ruler of Hell.
 * Lucifer is the only non-demon to date to rule over Hell, as he is an Archangel and the creator of the demons.
 * Overall, Crowley ruled Hell for the longest (8 years) during the show's run between 2010-2014, then again from 2015-2016 and again for a short period of time in 2017, while Azazel ruled Hell for the longest time, beginning at an unknown period of time prior to at least 1972 and ending in 2006.
 * Lilith ruled for two years from 2007-2009.
 * Lucifer ruled for one year in 2009-2010, than again for about a year in 2016 and retook control briefly in 2017.
 * Abaddon ruled in 2014.
 * Two out of the six known Rulers of Hell have been killed by Dean Winchester. He killed both Azazel and Abaddon (in that order).
 * Sam Winchester has killed one Ruler of Hell, Lilith.
 * Abaddon is the only demon whose death was plotted so that the throne of Hell could be vacant. Azazel, Lilith and Crowley were killed due to more personal reasons.
 * Hell and Heaven shared a ruler only once in 2016, when Lucifer took charge of both. This period lasted for about a day.
 * Abaddon is the only Ruler of Hell to rule for only one season.
 * Crowley is the only Ruler of Hell to have committed suicide.
 * Lucifer and Asmodeus are currently the only Rulers of Hell alive.
 * The Princes of Hell are the only species where more than one member has been a Ruler of Hell.
 * Sam Winchester has been nicknamed the "Boy King" (of Hell) by demons, although he has never taken up the moniker or the throne.