Born on the Citadel space station in a post-Reaper War era, he grew up during the galaxy's reconstruction effort. Because of his relationship to his famous father, Kaidan had a life of great privilege and affluence, causing him to struggle with his father's legacy and feeling pressure that was heaped upon him by others; these expectations fueled his desire to be acknowledged as his own person and not simply as Shepard’s son.

In 2198 CE, when he was eleven years old, Kaidan grew up during the early stages of the Great Galactic War between the Interstellar Republic and the Yahg Empire when the yahg launched a full-scale invasion, during which he was the target of multiple kidnapping and assassination attempts. Because of the threats against his life, Kaidan and his siblings were taken care of by their aunt and grandmother while his parents led the war effort. Later, several individuals, including Dr. Liara T'Soni, received a vision in which an older Kaidan was a prominent leading figure. As the batarians wanted to dominate the galaxy for themselves, they saw Kaidan as a threat to their plans.

While some initially expected him to continue the family tradition, Kaidan instead opted to join Alliance Intelligence and became one of AIS Director Miranda Lawson's top field agents. The batarians knew Kaidan as the Alliance codename Shadow, a name given to him by Balak after the youth assassinated two of the Revolutionary Order of Khar'shan's best operatives, Pranim Goccakk and Ran'gelor Craphi. At some point, he was reassigned to serve as the Intelligence liaison to the Normandy SR-2. Utilizing a mixture of stealth, firearms, hand-to-hand combat and biotic abilities, Kaidan often volunteered to lead infiltration teams to gather intel deep within the hostile Nemean Abyss. There, he disrupted the slave trade, killed a batarian warlord and was due to report back when he was captured by the extra-galactic targariums.

Kaidan spent nearly a year in captivity, during which he was tortured for weeks at a time. He escaped captivity and returned to warn the Alliance and Interstellar Republic about the oncoming threat, finding himself fighting on the frontlines alongside his father. In the final battle of the war, Kaidan defeated Emperor Rudali Mashan. For his efforts, he received an honorary promotion to the rank of commander and was given new orders to report for N7 training.

One week after his birth, he is held by his father and proclaimed that his son’s destiny was his own but that he would nevertheless be kept safe from any harm the galaxy’s horrors would try to inflict on him. He immediately became a matter of public interest, and news of the birth was spread throughout Citadel and Alliance space. In his youth, Kaidan and his younger siblings were raised mostly by Shepard, a respected public figure who has long since retired because of his injuries as an admiral. Ashley, meanwhile, remained in the military and was promoted to the rank of captain and was unable to be at home for long.

On one snowy morning, Kaidan and his siblings rushed to greet their mother who came home for shore leave, excitedly asking her to play with them.

A Hero's Legacy
The Scarlet Festival
Several years later, when classes at school were dismissed for the holiday, Kaidan and his brothers David and Ethan were seen taking a shuttle ride home with their friends from the Tayseri Ward. David complains about getting detention again while Ethan passes the time by trying to tell jokes, though Kaidan seemed to be preoccupied with preparing for the upcoming entrance exams for junior high school and wonders what tomorrow will bring. Soon, they are warmly greeted by their maternal grandmother. When the household receives a holo-vid from their mother, the boys were ecstatic to learn she was coming home for shore leave.

Great Galactic War
In 2198 CE, Shepard had a vision of his son Kaidan as a tall young man standing in the middle of a large crowd of mixed species, looking to him for guidance and peace, unifying the galaxy as his father once did. Javik had a similar vision, only this time Kaidan was surrounded by what looked to be his comrades-in-arms. When Liara saw this, she saw that he was among the friends who surrounded him and supported his goals.

However, when Ka’hairal Balak investigated, he was very displeased to see Shepard’s son, whom he believed that if any of his offspring rose to power, the batarians could never become the dominant power of the galaxy. After the yahg were defeated, Liara revealed that the envisioned Kaidan rising to power was the reason for the Great Galactic War.

Intelligence Operative
Kaidan soon graduated from high school and attended Oxford University. Upon seeing his aptitude scores, the Alliance offered him a full scholarship. He graduated early with high honors along with a dual bachelor's degree in psychology and master's in statistics.

Still wanting to follow his own path, Kaidan was recruited into Alliance Intelligence and would carry out several covert operations as a field agent. During his career, his superiors assigned him to assassinate two of the Revolutionary Order of Khar'shan's best operatives, Pranim Goccakk and Ran'gelor Craphi. He interrupted a meeting involving the ROK and captured a female batarian slave trader named Fasin Dad'roba in order to gain more insight into Balak's activities in the Terminus Systems.

[PERSONALITY AND TRAITS]:
Childhood
Kaidan’s personality is derived from both his parents, although Liara T’Soni noted that he takes more after his father than his mother. Being generally well-spoken, friendly and polite, he shows a great maturity for his age. Kaidan is also strong willed and determined like his mother; he even has a fascination of poetry.

At the same time, however, Kaidan has a fierce temper similar to his mother and is quite stubborn, often causing him to not back down from an argument unless proven otherwise. Kaidan apparently doesn’t like being teased, as he finds it irritating when he’s called "junior" instead of his given name. Despite their similarities, Shepard and Kaidan differ in a number of ways: whereas Shepard grew up as an orphan, Kaidan’s family is always there for him; whereas Shepard had no friends as a child, Kaidan has many friends; whereas Shepard had to work hard to get to where he was at, Kaidan's talents come to him naturally. Kaidan has a close attachment with his parents, having great respect for his father and was even pleased to hear from Liara, Tali’Zorah and Garrus Vakarian about how he physically resembled Shepard.

However, it is also shown that Kaidan has a close yet distant relationship with his mother ever since Ashley’s career as a soldier changed with her captaincy. He loves his mother and is overjoyed whenever they spend time together, but life in the military sometimes prevent Ashley from being around all the time. Although Kaidan is understanding of his often absent-mother, deep down he resents the idea of carrying on the Williams family tradition and opted to follow a different path than hers. Because of all this, Kaidan initially questioned the meaning of being a soldier due to the fact his mother’s duties kept her away from home for extended periods of time. Eventually, when Kaidan is finally exposed to the horrors of the Great Galactic War during the Scarlet Festival and realizes the sacrifices soldiers had to make, his relationship with his mother improves significantly.

Despite having let go of his disdain, he openly states that he has no intention of becoming a soldier, noting that it would just be another continuation of the Williams family tradition that his mother, grandfather, great-grandfather and great-great-grandmother have followed. He opts instead to walk his own path, carrying on his father’s resolve of protecting the galaxy’s newfound era of peace he helped establish.

Adulthood
By the time Kaidan is 24 years of age, he is very calm and composed even under pressure whilst maintaining a strong sense of morality. Although his exceptional intellect and extensive experience make him wise, they also make Kaidan slightly vain (depending on the situation), as he notably condescendingly calls the young, hot-headed Alliance recruit Raleigh Thorndyke "son" upon first meeting the latter. However, his ability to analyze a situation, plan his next move, and follow his better judgment allows him to escape dangerous situations both before and after they occur.

Thirteen years after the Great Galactic War, Kaidan still feels grateful for the presence of his surrogate aunts and uncles in his life, not just for their training, but also their love, protection and guidance. Though often contemplative, Kaidan lets such emotions smolder in his heart, reminding himself that he now has his own life to live and an important role to fulfill.

While usually serious and prim, Kaidan occasionally demonstrates a dry, sarcastic sense of humor.

[APPEARANCE]:
Kaidan has a light skin complexion and dark brown hair, both of which he inherited from his mother; in addition, he has the shape of his father’s face and blue eyes. He has straight hair with one side parted on the left side of his face while the other part is banged on the right side of his forehead. As noted by Liara T'Soni, he bears a striking resemblance to his father.

As a young adult, Kaidan stood at an impressive 6 feet and 1-and-a-quarter inches tall and is normally seen dressed in the most expensive and impressive outfits tailored from the most rated names in fashion.

[SKILLS AND ABILITIES]:

• Biotics: Having been designated as a biotic at a young age and personally trained by Jack, Kaidan can manipulate dark energy and create mass effect fields through the use of electrical impulses from the brain.
• Genius-level Intellect: From a young age, Kaidan demonstrated hints of being extremely intelligent, showing a keen and analytical mind on par with a salarian, which aids him in biological and other scientific-related knowledge as well as solving advanced mathematical equations and outsmart Samantha Traynor when playing chess (his childhood friend Andrea Taylor even noted he could easily pass advanced placement tests without cheating).