Morrigan was a Goa'uld Queen who hid her lineage from those around her, choosing to draw power towards her while remaining in the shadows of other Goa'uld and taking on the persona of the Phantom Queen. Moving slowly, Morrigan eliminated her rivals, including her former ally, Dagda, whose territory she claimed as her own. However, an attack by Heru'ur soon robbed her of much of her territory. For centuries Morrigan's territory grew slowly until the death of Heru'ur at the hands of Apophis allowed her to regain her lost territory and claim her place among the System Lords. She voted to let Anubis rejoin the System Lords, though her forces later joined those of Yu in opposing him. Morrigan later surrendered to Ba'al rather than be destroyed by the Kull warriors.
Born from one of the oldest Goa'uld Queens, Danu, Morrigan hid the fact that she too was a Queen from the very start. It was not this that set her apart from her brethren, but her cunning mind and capricious temperament. Indeed, when the rest of Danu's spawn were able to stop bickering long enough to strike down the System Lord Balor, it was Morrigan herself who planned the battle. Though Dagda and Manannan mac Lir split the spoils of the victory among each other, Morrigan was content to remain a power behind the throne, serving Dagda as a faithful advisor whom he could not do without. It was through this that Morrigan was able to sway the allegiance of many within the Goa'uld's court to her favour.
In addition to this, Morrigan was also able to position herself as the protector of her mother Danu, gaining further influence by expanding her control through the Queen. From this position of power, Morrigan found it relatively easy to spread rumours about her primary rival to power—Lugh. Bringing forth fabricated evidence that Lugh, who was a staunch advocate of Manannan and Dagda's alliance, had been plotting to kill Danu and her young, Morrigan demanded that she be allowed to punish him on her Queen's behalf. Though Manannan suspected, rightfully, that the evidence was false, he allowed the charges to proceed unchallenged as he and Lugh frequently disagreed on matters of military conduct. As such, Morrigan stripped Lugh from his host; rumours soon came about that she kept the symbiote imprisoned in stasis within her private apartments for many years to follow.
The power vacuum created due to Lugh's death was quickly filled as both Manannan and Dagda promoted new Generals from within their underlords. Dagda's replacement, the ambitious Cuchulainn, was very nearly the undoing of Morrigan's carefully laid out plans. As his host had been previously chosen to seed the Queen, Cuchulainn thus knew that Morrigan herself was a Queen; a secret Morrigan had been able to guard by mixing her own larva with that of Danu's at birth. However, Morrigan attempted to turn this liability to her advantage by offering him a place in her schemes against Dagda. Though she promised him much more power than he currently had in commanding a war fleet, Cuchulainn refused and scorned Morrigan as a "phantom queen" who lacked the power to make good on her offer. When this turned into Cuchulainn openly mocking her with the epithet, as well as privately threatening to reveal her secret, Morrigan knew she had to deal with the threat once and for all. As such, she arranged for Cuchulainn's flagship to be sabotaged during a critical battle. Though this battle was ultimately successful thanks to Morrigan's own planning, Cuchulainn did not live to see the victory he had brought about for Dagda.
Having eliminated her closest threat, Morrigan quickly turned her plans towards bigger things. Knowing that there was one more blow she would need to strike to become more than a mere phantom, Morrigan's thoughts were immediately put in place to take down Dagda himself. However, even Morrigan's own supporters were taken aback when Morrigan turned on her master during the midst of a council of his leading underlords, firing three blasts from a zat'nik'tel into his body which made it disappear forever. Claiming herself ruler of Dagda's realm, Morrigan fully expected there to be a time of temporary chaos despite her carefully laid plans which had guaranteed her the support from most of Dagda's underlords. She did not, however, predict that Heru'ur would launch a multi-front assault against her at the same time. Though she ultimately survived the assault, Morrigan was left with but a fraction of the territory she had worked so hard to acquire. Indeed, with the territory she then owned she could barely call herself a ruler; a place among the System Lords seemed further out of place to her now than it ever had.
Having learned her lessons well, Morrigan started to capitalize on every opportunity which presented itself to her through the incessant strife among the Goa'uld. She even took on the title of the Phantom Queen in a form of perverse pride, in order to spite the memory of Cuchulainn whom she considered an ungrateful fool who could have ruled beside her. For many centuries, Morrigan's territory grew aggravatingly slowly as she put her lessons to use until the re-emergence of the Tau'ri created a sudden power vacuum. The death of Heru'ur at their hands helped her significantly and, though she would have preferred his death to be at her hands, she quickly took back the territories he had stolen from her many years ago. Morrigan's power could no longer be denied, and she was finally admitted into the ranks of the System Lords.
Due to the fact that Morrigan's territory, unlike the rest of Danu's children, was close to that of other System Lords, she became the de facto spokesperson for her brethren, representing them before the other Goa'uld; this position only gained her more power. Luckily for her, of the Goa'uld she spoke for only Manannan was powerful enough to oppose her and he was more than happy to let her take the forefront while he remained hidden in the shadows. Morrigan's run of good luck was not to last forever, however, as she—along with the rest of the System Lords—had a dip in fortune with the reappearance of Anubis. (RPG: "Living Gods: Stargate System Lords")
When a summit was called among the highest ranking Goa'uld, Morrigan was one of only eight to make her way to the Hasara space station in the Hasara system. While there, the Goa'uld discussed the attacks they had all been subject to from an unseen aggressor. The council was interrupted, however, when Osiris entered the room and informed them all of the identity of their attacker—Anubis. Seeing few alternatives, Morrigan was one of the many who voted to reinstate Anubis into the ranks of the System Lords. (SG1: "Summit", "Last Stand") However, she soon regretted this vote as Anubis retrieved the Eye of Balor from Morrigan's own planet of Magtireth, which had been where Balor's ship had been destroyed many years ago. What puzzled Morrigan more than anything was how Anubis's agents had managed to find the jewel, as she had believed it lost. (RPG: "Living Gods: Stargate System Lords")
It was soon after the summit that Morrigan chose to visit the planet Gleanavar, one of the many under her domain, by ha'tak. At the same time, however, SG-17 were visiting the planet to meet with Sholred, the undercover Tok'ra agent acting as Morrigan's underlord on Gleanavar. Morrigan's Jaffa managed to capture two of the SG team who were hiding next to the Stargate and brought them to Sholred's temple. At the same time, Morrigan had used Transportation rings to visit the temple herself, interrupting the festival which was taking place. When the two members of SG-17 were brought in, Morrigan attempted to use her kara kesh to reveal the location of the rest of their team. Unfortunately for the other members, their names had been heard by Mek'nar who reported this information to Morrigan. The other members of SG-17 soon revealed themselves to Morrigan and, though they were able to insult her, Morrigan's Kara kesh soon shut their mouths. It is unknown what happened to Morrigan on the planet after this event, as Sholred started a rebellion on the planet before escaping with SG-17 through the Stargate. (RPG: "Tightrope")
Ultimately, however, Morrigan did survive and instated Evnith to replace Sholred as the ruler of Gleanavar. Later, while Lord Yu was the representative of the combined System Lords, Morrigan added her ha'taks to his forces without question when they gathered to attack Anubis' mothership over Abydos. (RPG: "Living Gods: Stargate System Lords") Though she did manage to survive Anubis's return, Morrigan was forced to surrender her forces to Ba'al when he took control of the Kull warriors. What happened to Morrigan after this point is unknown, though it is possible she simply entered into Ba'al's service as many defeated Goa'uld before her. (SG1: "It's Good to Be King")
Much like the other Goa'uld, Morrigan's Human subjects view their god as an object of adoration and fear, whose passions and indeed very form are as interchangeable as the wind. Many of these people, much like their brethren in Dagda and Manannan's service, were originally descended from the Celts of what eventually became known as western Europe and the British Isles on Earth. As such, these people viewed Morrigan as the Mother of all things, sovereign of life, death, and rebirth; on the worlds which Morrigan took from other Goa'uld, she created propaganda which showed the previous god to be but a child of Morrigan's who had erred from her path which she had to punish.
In keeping with the existing legends of the god she was impersonating, Morrigan chose to add an additional layer of mystery to the standard Goa'uld means of impressing the populace. While other Goa'uld often chose one host and stuck to it, Morrigan had many hosts hidden throughout her empire, kept in stasis in sarcophagi until they were needed. As such, her people were often unsure which guise they would see their god in and were not surprised to see an entirely new face. Because of this, Morrigan often posted underlords on her worlds who would impersonate her, both giving her the appearance that she was always on that planet as well as the appearance of being able to be in more than one place at once; a true sign she was a god. Though it delighted Morrigan to appear in many different guises, her favourite and most common host was one who presented her as the Celtic ideal of power and beauty; a red-headed woman of regal complexion.
From her birth, Morrigan tried to hide the fact that she was a Goa'uld Queen, knowing that it would curtail her autonomy if the System Lords ever found out. Indeed, as the years went on and Goa'uld Queens grew all the more rare, Morrigan only fought harder to keep her secret. Ever since gaining the persona of the Phantom Queen, rumours started to spring up that she was in fact more, a real Queen. Morrigan was quick to stop these rumours when she could, killing those who spread them. To keep the secret safe, Morrigan did not even tell her most trusted slaves the entire truth, as Morrigan kept Danu close to her so that she could pretend her larvae were that of the older queen. In truth, Danu stopped giving birth long before Morrigan rose to the rank of System Lord. Though not a permanent solution, Morrigan could not think of any other solution.
Despite being considered somewhat of an upstart by her fellow System Lords, the depths of Morrigan's strategic experience over the years far surpasses many of the Goa'uld who held greater power than she. Having learned from her mistakes, Morrigan chose the targets for her attacks carefully, gathering intelligence on them before laying a trap which would cut them off from their support to take full advantage of their vulnerabilities. However, these elaborate plans often meant that Morrigan had to choose precisely the right moment to attack; a flaw which her volatile temper was often known to interfere with. Perhaps because of this, Morrigan learned not to commit too many of her resources at any one time no matter how sure she was of the outcome. Because of these traits, most of Morrigan's Raven Guard thought themselves to be more loved by their god than other Jaffa were by theirs. (RPG: "Living Gods: Stargate System Lords")