Dead Three

The Dead Three, also known as the Dark Gods, was a collective of three, death-themed deities: Bane, the Lord of Darkness, Bhaal, the Lord of Murder and Myrkul the Lord of Bones. Originally, they were powerful mortal adventurers who sought the path to godhood, known at first as the Dark Three. They found it in the form of Jergal, who acquiesced to their demands as he was tiring of his life as god of the dead. He gave up his portfolios to the three of them, apotheosizing them in the process. Bane ruled tyranny and strife, Bhaal became the god of murder & Myrkul, the dead.

They earned their name of the Dead Three when they all perished during the Time of Troubles. Bane and Torm killed each other in 1358 DR, Myrkul was killed by the mortal mage Midnight while Bhaal was slain by Cyric, using the sword Godsbane, an avatar of Mask.

Mortal life
In the mists of the past, the Dead Three were three power-hungry mortals: Bane the tyrant, Myrkul the necromancer, and Bhaal the assassin. The three forged a pact to achieve godhood or die trying. With their eyes on the ultimate prize of the portfolio of Jergal, Lord of the End of Everything. The three traveled the lengths of Faerûn, endured epic quests and obstacles until they finally destroyed one of the Seven Lost Gods and took a portion of its divine essence for themselves.

With this small portion of divine power the three powerful, but still mortal, companions traveled to the Gray Waste and sought the Castle of Bone. They battled through seemingly endless hordes of undead including skeletons, zombies, spectres, wraiths and even liches. After defeating the legions of Jergal's minions they came upon the mighty god upon his throne of bone.

Immediately the Dark Three claimed the throne as their own, bickering for a moment before the God of the Dead addressed the companions. Much to their surprise, Jergal willingly stepped aside, claiming that he was happy to grant his powers to one of the trio. He offered his guidance to the new ruler, until they were ready to oversee the dead on their own, then asked which among them would take their seat on the throne. At this point they returned to squabbling and a fierce fight broke out between the former friends. Indifferent to their wants, but not wanting to see them battle for eternity or die from exhaustion, Jergal resolved their dispute with a game of skill.

While a failed game of "skull bowling" led nowhere, in part due to the intervention of the god Malar, Jergal suggested leaving the decision up to Lady Luck. He proceeded to break off his skeletal finger bones and the three dark travelers proceeded to play a game of knucklebones. Bane emerged as the winner and took on the divine portfolio of hatred, strife, and tyranny. Myrkul, who came in second place, took reign over the dead and Bhaal was left with dominion over death and murder.

Their ascension was recorded in the book History of the Dead Three.

As deities
The Dead Three reigned over their respective realms for many years. True to his word, Bane spread hate and tyrannical rule across Faerûn, inspired a network of zealous wizards and thralls in the Zhentarim during the 13 century DR, and within a century later would come to be one of the most hated deities and face of evil across the continent. Myrkul never enjoyed the widespread, dreadful veneration as was found among the followers of Bane but he was given constant offerings at funerals, by mourning loved ones full of fear and sorrow. Bhaal on the other hand had become a god of immense power, having garnered the servitude of Loviatar and Talona in the divine realm and the voracious beast Kazgaroth, an aspect of Malar, in the Moonshae Isles on Toril.

In the year 75 DR, the great seer Alaundo arrived at the library fortress of Candlekeep, where he presented the monks with his many prophecies. Among them was a vision that Bhaal would become aware of his imminent death as a god and ensure his legacy by sowing his seed across Faerûn, with little to no regard for his partners. Alaundo's divination was true, and by the mid-14 century, Bhaal had spawned a score of mortal progeny.

Bane also saw his influence on Toril extending beyond his his existence, though the creation of his offspring was somewhat less prolific. Sometime before 710 DR, the half-fiend known as Iyachtu Xvim was spawned as a result of the union between the Black Lord and a true tanar'ri and walked onto Toril through an Abyssal portal in Westgate.

Time of Troubles
Consumed by greed for even more power, Bane and Myrkul conspired together to steal the Tablets of Fate from Lord Ao. Frustrated with the deities' growing apathy and abdication of their duties, Ao struck down all the gods to weakened forms of their respective avatars, sending the Tablets to the world of Toril and ushering in the Time of Troubles as well as the dawn of the Era of Upheaval. The reign of each of the three Dark Gods came to an end during this time, at least temporarily.

After the avatar of Bane appeared on Toril, he rallied his clergy and agents of the Zhentarim and began to hunt down the Tablets of Fate. He was joined in this endeavour by his fellow former allies, Myrkul and Bhaal. While the tyrant originally assaulted the town of Shadowdale, which ended in a battle with Elminster and <ystra, he eventually discovered the location of one of these artifacts, guarded by the avatar of Torm in the Temple of Torm's Coming in the city of Tantras.

Myrkul appeared in West Faerûn and he proceeded to travel to the Chauntean temple of Goldenfields in the Sword Coast North. The avatar of the God of Death was defeated in battle by the High Priest Tolgar Anuvien, a feat which nearly killed the former Crazed Venturer. Sometime after this battle, Myrkul learned of the location of one of tablets, reclaimed the artifact and brought it to his realm of the Great Waste of Hades.

On Eleasis 13 1358 DR, As the forces of Zhentil Keep prepared to invade the city on the coast of the Dragon Reach, Myrkul had his clergy work on a mass-scale death spell. Having gained the true names of all the assassins of Faerûn, his worshipers killed scores of followers of Bhaal in a single moment. Meanwhile the priests of Bane performed a ceremony known as the Stealing of Souls, which allowed them to harness the great amount of life force that had been released at once.
 * Battle of Tantras:

As a result, Bane's essence was transferred from his avatar to the colossal, massively-armored statue of black glass that was known as the Black Brother. The gargantuan aspect of the Black Lord marched over the Dragon Reach towards the city of Tantras, to claim the found Tablet of Fate, it was met by a titan-sized, lion-headed Torm. The True Deity had himself been empowered by thousands of lives, offered in sacrifice by the faithful of the city, given upon their god's request. As the two gods battled over the the coastal city on the Reach, chain lightning shot from their massive blows upon one another and the earth beneath them shook as if the Toril was being torn asunder. Just as the Bell of Aylen was rung in the southern end of the city Bane and Torm destroyed one another in a blast of silver radiance, followed by a massive explosion. The tablet was recovered by the adventurers Midnight, Kelemvor and Adon,

Having just betrayed his friends Kelemvor and Midnight in events just prior to the deaths of Bane and Torm, the mortal Cyric sought the tablets for himself.
 * Waterdeep:

Aftermath
However, the Dead Three have proven difficult to destroy. Bane has returned from his grave, having sired Iyachtu Xvim as a sentient cocoon from which he recently emerged, restored to near-full power. Myrkul is known to be inhabiting the evil artifact, the Crown of Horns, whereabouts unknown, but certainly plotting his return to godhood. Bhaal, who foresaw his own demise, fathered scores of children during the Time of Troubles as part of a scheme to return to power, the details of which are central to the plot of the Baldur's Gate series.

Further information regarding Myrkul can be found in Neverwinter Nights 2: Mask of the Betrayer.

It appears that dead gods still have consciousness so long as mortals worship or fear them. In Myrkul's case he still has a following which sustains his consciousness. In addition the player character learns that he is harboring the soul of Myrkul's High Priest, Akachi The Betrayer, who led a revolt against Myrkul for sentencing his love to the wall of the faithless for not believing in a god. Akachi's punishment was to be himself placed in the wall of the faithless until the wall had consumed the memories and identity of his soul but not the entire soul. Then his soul was removed in placed into a mortal body in Rasheman where all it knew was the insatiable hunger to feed on other souls, primarily the spirits that are abundant in Rasheman but also, eventually, the person that it was inhabiting as well. Meanwhile, while the player character's body is inhabited by Akachi's soul, the player character's soul went to the spot in the wall of the faithless where Akachi's soul should be. This all leads up to the player character meeting the dead god Myrkul and possibly using his devour soul ability on the dead god, thereby ending his consciousness and finally killing the god.