Spencer Illéa, Gregory's oldest son, was about to become the king of Illéa after his father would retire. However, he soon realized that his father had forced his older sister Katherine to marry the King of Swendway so that he could become the king himself. He knew that the same was expected of him, but he couldn't do it. So he faked his own death and ran away, although his father suspected the truth and wrote about it in his diaries. His younger brother Damon Illéa became the king instead. Spencer hid with relatives and friends, eventually making a camp with some like-minded people in the north and becoming the founder of Northern rebels. The majority of Illéa's people believe that Spencer really died and after the death of Justin Illéa, the family was extinct. The Northern rebels though and those who have read Gregory Illéa's diaries, such as America Singer, Prince Maxon and King Clarkson, know the truth: August Illéa is the great-grandson of Gregory and the true heir to the crown. It is hinted that there are also some other relatives of him, but their number is unknown.
Maxon was prepared that one day one of Spencer's descendants would come for the crown. On night that the king was in a business trip to France, August and his fiancée Georgia Whitaker came secretly and unarmed to the palace, demanding to speak privately to Maxon and America. Although August admitted that he was a direct descendant and legal heir to the throne of Illéa, he declared that he didn't want to be the king. On the opposite, he respects the monarchy and especially Maxon. He simply supports the goals of the Northern rebels: having nominated officials and putting an end to the castes. He also reveals that the Southern rebels do want to kill off the royal family, take over Illéa, and leave all of the people in the lower castes in the same place they are now, although making promises to change their life. The Northern rebels are the only who can fight against them and protect the country and the royal family. Thinking that Maxon and America are already in love and considering that America would be a great queen as she helps the people in need and supports the ending of castes, August asks from him to marry her. Maxon becomes furious though, because he is tired of so many people pressing him who to choose. The two men reconcile soon however, promising to meet again soon.
Later, they meet again in the darkness outside the palace. Maxon asks him if he has information about how many people were killed by the Southern rebels. They draw the conclusion that the Northern rebels need weapons to have better opportunities to stop the Southern rebels and be trained. After the meeting, August, Georgia and Micah come to help Maxon, Aspen and Avery because Southern rebels attack them.
Their friendship got deeper after the Northern rebels helped the people in the palace from an attack of the Southern rebels at the end of The One, essentially saving the life of Maxon and Aspen Leger.
In The Heir it is mentioned that August helped Maxon to stop the Southern rebels.
In The Crown it is revealed that August was helping Maxon dissolve the castes, but after he complained that it wasn't dissolving fast enough they both ended up having a huge argument. Eventually he and Georgia packed up their stuff and their son and left the palace; ever since then they have been on cold terms with the Schreaves.
August is described as tall, slim and blond. He wears boots and clothes that a Seven might wear. He also wears a rusting compass on a long chain around his neck, a symbol of North Star. According to America, when she first saw him, "he looked rugged without being terrifying".