It is revealed in a Court of Mist and Fury that Keir, Morrigan's father, in an attempt to woo the Autumn Court into an alliance, offered his daughter Morrigan's hand in marriage to Beron's eldest son, Eris. Due to Eris' reputation for cruelty, Morrigan decided to lose her virginity to Cassian, a bastard-born Illyrian, so that she would not have to marry Eris. When Eris hears of this, he refuses to marry her, claiming that she had been "sullied by a bastard-born lesser faerie," thus ruining Keir and Beron's fragile alliance (it is revealed in A Court of Wings and Ruin that this excuse was designed to give Mor an 'out' from an engagement he knows she does not want). In response, Morrigan's family left her on the Autumn Court border stripped naked, having been tortured by them, with a note nailed to her body that announced that she was Eris' problem. Eris, however, ignored her and left her in the middle of the woods to die. 
In A Court of Wings and Ruin, Eris and his brothers happen upon Lucien and Feyre, who had just fled from the Spring Court and were traveling to the Night Court on foot until they regained their magic. Feyre and Lucien manage to escape their clutches, and Eris and his brothers subsequently attempt to hunt them down. However, Feyre and Lucien manage to make it to the Winter Court borders and are then rescued by Azriel and Cassian. Eris and his brothers are overwhelmed and bested by the Illyrian warriors, but Feyre, however, decides to spare them. The Autumn Court sons flee back to their homeland relatively unscathed.
Later on, Eris allies himself with the Night Court, however slightly. Hungry for power and his father's throne, he strikes a deal with Rhysand. In exchange for his help in seducing Keir into an alliance with Rhysand against Hybern, Eris was guaranteed Rhysand's support should he decide to overthrow his father and claim his father's throne. During the course of the novel, Beron's support of the resistance toward Hybern fluctuates, and it is considered by the Night Court to kill Beron and crown Eris, earning a more steadfast ally. Ultimately, Beron does decide to support Rhysand and aides the Night Court and their allies in the final battle against Hybern in the Mortal Lands, albeit after being threatened and practically forced by Tamlin.
Eris also claims to have refused to participate in the torture and death of Jesminda, Lucien's lesser Fae lover, and also that it was he who saved Lucien's life later by alerting Tamlin to his presence near the Spring Court border. Tamlin then saved Lucien from his brothers and Lucien defected to the Spring Court. He also claims to have ended his engagement with Morrigan because he knew she did not desire the union, not because of his disgust at her union with Cassian. All of this, however, is unsubstantiated claim.
Eris is a High Fae and, as the eldest of Beron's sons, he is presumed to be the heir to the Autumn Court.
Eris projects an air of arrogance and entitlement and can be antagonistic and violent at times. However, from the things he says and hints in the text, it seems there are deeper layers to him that reflect compassion, caring, and even true kindness at times. It is implied that his ruthlessness is a by-product of growing up under his father's cruelty, as well as having to constantly contend with his scheming younger brothers to avoid being betrayed and murdered by them in their quest to seize his position as heir. Like Rhysand, Eris appears to play-act to achieve his goals.
Although he has done many bad things in his life, Eris confessed in A Court of Wings and Ruin that he had no part in the execution of Jesminda, Lucien's lover, and that he had even alerted Tamlin to save his brother. Eris admitted that he had ended the engagement with Morrigan long ago because she did not want it. This shows his motives are sometimes benevolent, and that he is rather perceptive. It is a possibility that Eris pretends to be such a cruel, ruthless Fae due to being born into the Autumn Court, and sired by Beron. When Eris takes over as High Lord of the Autumn Court, it is unclear if he will continue his facade or drop it.
- A Court of Thorns and Roses (1st appearance)
- A Court of Mist and Fury (mentioned)
- A Court of Wings and Ruin
- A Court of Frost and Starlight
- A Court of Silver Flames
- A Court of Mist and Fury: Chapter 41
|Amarantha · Amren · Azriel · Cassian · Elain Archeron · Feyre Archeron · King of Hybern · Koschei · Lucien · Morrigan · Nesta Archeron · Rhysand · Tamlin · Vassa|
|Minor and supporting characters|
|Alis · Andras · Beron · Bron · Cerridwen · Clare Beddor · Cresseida · Devlon · Eris · Graysen · Feyre's father · Hart · Helion · Ianthe · Isaac Hale · Isaac Hale's wife · Jurian · Kallias · Keir · Mercenary · Miryam · Mortal Queens · Mrs. Laurent · Naga · Nuala · Unnamed Summer Court Faerie · Tarquin · The Bogge · The Bone Carver · The Suriel · Thesan · Tomas Mandray · Varian · Weaver|
|Aunt Ripleigh · Dark Mother · Drakon · Feyre's mother · Ianthe's father · Ianthe's mother · Ianthe's sisters · Miryam's father · Miryam's mother · Mother · Rhysand's father · Rhysand's mother · Rhysand's sister · Nostrus · Queen of the Black Land · Tamlin's mother · Tamlin's father|