Anankos also known as the Dragon of Wisdom is a Silent Dragon, the true main antagonist and final boss of Fire Emblem Fates and he was also responsible for creating the imposter Garon who was tasked with ruling over Nohr for him and possessing Takumi in each events. Once revered as one of the First Dragons, his degeneration resulted in the obliteration of both Valla, almost all of its people and his own sanity. he is also the father of both Lilith and Corrin.
Anankos is one of the First Dragons, also known as the Dragon of Wisdom. Anankos loved humanity and gave them longevity and knowledge. Anankos became particularly close to the kingdom of Valla and started to live among its inhabitants. He was also a particularly close friend of Cadros, the first king of Valla. To a select few, he gave the essence of his blood, allowing them to utilize the power of Dragon Veins, a trait that was passed down through the Vallite royal bloodline.
However, as with the other First Dragons, he began to degenerate over time. Unlike the other First Dragons, Anankos did not shed his mortal shell, opting to stay behind as a figurehead for the Vallite people. Through the power of a song and a fragment of his dragonstone, both of which were passed down through Vallite royalty, his urges could be quelled. However, after many generations of kings, Anankos' rage grew strong enough for him to burn down a forest. The people of Valla blamed him for it and tried to kill him.
Unable to comprehend that the very people he had helped had betrayed him, Anankos locked himself away in a mountain cave, where his detest of humanity grew. The King of Valla and a few select people would make trips to his cave to express their belief in him. Unfortunately, he lost control of himself and killed the King of Valla of that time. Before he completely degenerated, he tore off a portion of his soul, which took on a human appearance in a last bid to stop his rage. Anankos then began to form an invisible army consisting of many of his former Vallite subjects. He even began to resurrect the dead to strengthen his army. He also self-sired a daughter named Lilith to further his goals.
The human avatar wandered with no memories of his past and soon met Mikoto. The two fell in love and eventually gave birth to a child. However, soon after the birth of his child, he recovered his memories and sent them away from the kingdom to spare them from the ruined kingdom. He made Mikoto promise to never tell their child of their father to spare them from the burden of his past sins. With his newfound clarity, he had a vision of another world where many heroes felled a great dragon. He desired to seek help from the warriors of that world.
Anankos transported himself to another world and arrived in Ylisse some time after the fall of Grima. He called out for anyone to help him, and the message was received by Owain, Inigo, and Severa. Bringing them to the Mila Tree, he asked for their help by coming to their world and the three agreed to, before Vallite forces sent by his dragon form ambushed them.
After defeating the Vallite forces sent by his dragon form, Anankos thanked the three for helping and offered to fulfill any request they desire. Initially, the three hoped that Anankos could resurrect their fallen parents and friends from their original timeline; however, Anankos could not fulfill that request. Instead, they asked that the original world be beautiful once more and that their parents and friends would have proper graves, which Anankos does for them. Before they leave for Valla, Anankos finds a Fell Brand, presuming that it came from the tactician of that world.
Upon bringing them to Valla, he is given time to explain his story to them. He makes a request for them to head to Hoshido first to see Mikoto and help his child fulfill their destiny to assemble the five divine weapons to take down his dragon self. Before he can tell them of his child's name, Lilith appears under orders of Anankos' dragon self to stop him. Shocked by the news, she informs him that his child had been taken to Nohr. Owain, Inigo, and Severa attempt to attack Lilith, but are unable to do so. Anankos had a vision prior to their arrival showing that the three would be defeated if they met a girl in Valla. Anankos offers to send them back home, but the three refuse and choose to stay and fight. After they encourage him to believe in them, Anankos gives them the power to defeat Lilith and bestows onto them their new names: Odin, Laslow, and Selena. The three manage to escape.
Lilith continues to summon more soldiers to fight, but Anankos warps the three heros to Nohr and tells them to become retainers for the Nohrian royal family in hopes of finding his child. Left alone to deal with Lilith, the young girl tries to kill Anankos' human avatar, but finds herself unable to do so. Anankos tells Lilith that he really does love her despite just meeting her, but Lilith remains conflicted because his dragon form never expressed that same sentiment with her despite her efforts to please him.
When she finally decides to abandon her attempt to murder his human avatar, the dragon Anankos senses his daughter's wavering and attempts to kill her. Sensing this, Anankos sacrifices himself, taking the hit in her place. As he slowly dies, he asks Lilith to smile for him as he speaks his final words, apologizing to Lilith, Mikoto, and his child. Back in the Vallite Castle, Anankos swears to start a war between Hoshido and Nohr and end the human race. However, a fragment of his human avatar speaks through him, expressing his belief that Selena, Odin, and Laslow will one day bring Corrin to him and defeat him.
By the events of Fates, Anankos has become completely insane, acting as a tyrant and killing nearly everyone across Valla. Those that survived were enslaved in his mad lust to destroy humanity for abandoning him to his pain. He also gains control of Nohr through King Garon, whom he possessed and gave a portion of his power. He also resurrects King Sumeragi, the fallen king of Hoshido, and has him act as his assasin who eventually assassinates Mikoto with Ganglari, thus instigating the war between Hoshido and Nohr.
In the Birthright route, Anankos gives Garon additional power, transforming him into the Dusk Dragon in a final attempt to kill Corrin's party, but this fails and he loses a significant portion of his power but is never trully killed.
In the Conquest route, Ganon's body is destroyed by Corrin's party so he possesses Takumi's body in a final attempt to kill Corrin's party; however, this also fails and Anankos is forcefully driven out of Takumi, who truly dies shortly afterwards.
Throughout most of the Revelation route, Anankos possesses Gunter. Gunter acts as Corrin's servant but try to assasinate him multiple times when he is alone, one of those attempts result in Scarlet's death. Towards the end of the game, Anankos is exposed and finally fights the party in the throne room as Gunter. After being defeated, Anankos is exorcised from Gunter by Azura's singing and Gunter stabbing himself after Corrin managed to speaks him out of the possession. Anankos' spirit actually regain his body and the Dragon is awakened and fight the party by himself but is finally defeated by the united army.