Nothing is known about Aiden's life before the outbreak began except that he has a father Reg Monroe, a mother Deanna, and a brother Spencer. He was also in the ROTC and was close to receiving a lieutenant's commission.
When the plague started, Aiden was with his parents. With his mother being a congresswoman, they were expected to come back to Ohio to help the district manage the crisis caused by the epidemic. However, he and his parents were stopped by the US Army and directed to a community in Alexandria for safety. After a while, the army never arrived in Alexandria, leaving Aiden and his family, along with other refugees, to build walls around the community. Using construction materials from an unfinished shopping mall nearby, he helped his dad build a perimeter, and as more people arrived, they assisted the Monroes in the completion of the wall.
A month prior Rick Grimes and his group's arrival to the Alexandria Safe-Zone, Aiden was scouting with Nicholas and four other runners in a town not far from the community. Unfortunately for the scouting party, they were attacked by walkers and the four runners were killed, leaving Aiden and Nicholas as the only survivors. In retaliation for the walkers killing their friends, the men began trapping and tying up walkers to be killed before supply runs.
Aiden and Nicholas meet with Tara Chambler, Glenn Rhee, and Noah in order to train them as runners for future missions. While out in the woods, Aiden explains to the newcomers that they are to follow his instructions. They soon approach a bloody rope used to restrain a walker, which had escaped. The men start making loud noises to lure it, much to the dismay of Tara, Noah, and Glenn. When the walker emerges from the bushes, Nicholas and Aiden attempt to capture it. Tara tries to help, but the rotting walker proves too much, causing Glenn to step in and stab it in the head, angering Aiden. Back in town, Aiden confronts Glenn, which turns physical and ends up with Aiden being punched by Glenn until his mother steps in and orders Aiden to back off.
Aiden and his team of runners (including Eugene Porter) lead an expedition to a storage warehouse. Before leaving the walls of Alexandria, he exchanges a few words with his parents, each of them worried about his safety. He tells his father to take care, to which his father states that he should be the one to tell Aiden the same.
Upon their arrival at the warehouse, Aiden is quick to point out their fastest route, in and out, before Glenn tells him that they should scout the perimeter to find all their exits if things were to go awry, to which Aiden agrees. Once their reconnaissance is over, the group discovers a group of around two dozen walkers trapped behind a chain fence. Aiden, looking unnerved by the number of walkers, compliments Glenn's knowledge and strategies, and suggests they get to work. While pairing with Nicholas, he turns to find that he is being followed by a single armored walker, and began to shoot it several times, once in the leg, in attempt to stop its advances. Despite Glenn's protesting, Aiden impulsively continues shooting, accidentally hitting a grenade on the walker's bandolier, causing an explosion that severely injures Tara and impales him on a shelf, knocking him unconscious. Nicholas pronounces him dead and has the others leave his body in the interest of protecting Tara.
While the others tend to Tara's injuries, Aiden comes to, alerting the bunch, to which Glenn calls on Nicholas and Noah to help retrieve him from the debris. Aiden is then comforted by Glenn before his and Nicholas' attempt to remove him from the impalements as walkers close in on the four. After their struggle to remove Aiden, Nicholas leans in towards Aiden, whispering to him that the two left their friends behind on runs to save themselves, saying it was how they were, before running off to save himself. Glenn, still convinced he could save Aiden, tries one last time to remove him from his fate, to which Aiden reveals that he had gotten the four former runners killed because he had broken the rules of his own system. He then tells Glenn to stop his attempts at saving him, before Noah pulls Glenn away, leaving Aiden to be swarmed by the walkers, who then proceed to tear open his stomach and eventually kill him.
Aiden is knocked back by an exploding grenade and impaled on two metal bars of a storage shelf after shooting a walker. Despite trying to help him, Nicholas panics and leaves. Glenn tries to save him by himself, but with walkers closing in, Glenn and Noah are forced to flee, leaving Aiden to be devoured by the walkers.
The two men aren't seen interacting but it is assumed that Aiden's father, Reg Monroe, was very saddened when he found out about his son's death. He is seen in tears with his wife and other son on the night of the incident.
Deanna and Aiden have a basic mother and son relationship. Aiden is shown to respect his mother, but somehow Deanna sees through his recklessness. Aiden is known for being a bully by using his power inside the community which is run by his mother, and Deanna is aware of that. When the fight between Aiden and Glenn ensued, Deanna thanked Glenn for punching her son in the face, further proving that Deanna sees the bad qualities inside her own son. Following his death, Deanna seemed sorrowful at the news, and even played one of his mixtapes over their stereo, showing that despite his traits, she still loved and missed him dearly.
"What happened to dad? To Aiden?! That's all you!"
—Spencer blaming Deanna for the deaths of Reg and Aiden.[src]
Though the two were never seen interacting with each other on-screen, Spencer and Aiden were implied to have shared a brotherly relationship. Following Aiden's death, he and his parents mourned him in silence. When Deanna chastizes him for raiding the pantry, Spencer blames her for the deaths of both Reg and Aiden, showing that he cared deeply for the both of them.
Nicholas and Aiden appeared to be an efficient team and dual-minded in their behaviors. It is implied through a few conversations between Deanna and Rick's group, as well as Aiden's conversations, that he and Nicholas knew each other prior to the outbreak, though nothing is confirmed. The two had the same desire to teach the new people about how they perform supply runs. Aiden and Nicholas coordinated to try and ensnare a single walker that had killed their friends. After it was killed by Glenn, they returned to Alexandria and both attacked Glenn and Noah, though the fight was ended by the intervention of Rick, Michonne and Deanna. Aiden and Nicholas were both reprimanded for their reckless actions, but were not particularly punished.
After Deanna's forced integration of Rick's group into the community, Aiden and Nicholas seemed to tolerate their new team a little more, though they both continued to have the same, reckless behavior. Aiden and Nicholas broke off into a group of two as per their plan to search the storage warehouse. After the explosion accidentally triggered by Aiden, Nicholas pronounced him dead after seeing him impaled on a shelf, though he valued his own life such that he did not try and actually check to see if he was still alive. After Aiden cried out in pain and shouted for help, Nicholas was reluctant to aid him, but used his flare to distract the walkers anyway. He and Glenn attempted a rescue, but Nicholas marooned them for fear of being killed by walkers. Nicholas showed no real reaction to Aiden's death.
"Hey...hey! Look, we got a way doing things around here-- it killed our friend! (...) Look, I'm not having this conversation. You will obey my orders out there! (...) Say that again. Come on. Come on, tough guy."
Glenn and Aiden met a few days after Glenn and his group entered Alexandria. They started off smoothly, and they respected each other, until Glenn started seeing how he deals with the walkers, one of which almost bit Tara. Aiden tried to warn Glenn how they do things at Alexandria, which Glenn disapproved of. Aiden asked his mother why she let Glenn and his group in before trying to punch Glenn in the face, only to be knocked to the ground in the attempt.
Apparently, Deanna's forced integration of Rick's group turned their relationship for the better, as the two seemed to listen to each other when raiding the warehouse. When inside, Aiden impulsively shot an armored walker several times, one of his gunshots hitting a grenade and impaling him on a broken shelf. Glenn tried to save him with the aid of Nicholas, but was unable to due to Nicholas' desertion. Glenn was then forced to try to save him alone, but Aiden told him not to because he did not want to get another person killed, revealing that he had gotten his last team killed. Glenn was dragged away by Noah shortly before the walkers killed Aiden, greatly saddening Glenn.
Aiden and Tara did not directly interact very much, but during their brief encounters, they were very uneasy around each other, and even hostile at times. When Aiden and Nicholas tried to tie up a walker for a ritualistic "pregame", Tara was almost killed because Nicholas and Aiden lost control of the situation. Tara was only saved by the intervention of Glenn when he killed the walker, which made Aiden furious because Glenn and Tara had interfered in his plans. After Deanna's forced integration of Rick's group, Tara went back on another, more serious, supply run with Aiden. Aiden showed little care for Tara's or anyone's safety when he impulsively fired repeatedly at an armored walker, accidentally hitting a grenade with one of his gunshots. The explosion severely injured Tara, knocking her unconscious. How Aiden's death will affect Tara remains to be seen, as she was not conscious to either hear of his passing or present to witness it.
Noah and Aiden started well. They respect each other, and when Noah brought up that his father was once did the same job as Aiden did, Aiden asked him whether or not his father made it, to which Noah answered that he did not. Aiden appeared to be saddened, as he sincerely says he is sorry about what happened to his father. Aiden then had Noah hold his fire when trying to ensnare a walker.
After Deanna's forced integration of Rick's group, Noah went on another supply run with Aiden. Aiden complimented Noah's accuracy after the latter killed a walker at a moderate distance with a quick draw of his pistol. When Aiden accidentally triggered an explosion, Noah did not visibly grieve for the man he presumed dead due to Tara's life being in danger. Once he realized Aiden was still alive, he went to save him by keeping the walkers occupied while Glenn and Nicholas went to work on getting him off a shelf. Once Nicholas abandoned the effort, Noah was forced to drag Glenn away just before the walkers arrived. It is unknown exactly how Noah felt about Aiden's passing, due to he and Glenn being forced away from him in a rush, as well as him meeting his own untimely demise just mere minutes later.