Athan is the son of Cassandra Railly and James Cole. He was born in 2047 and lived his entire life dislodged from time. Athan was raised by the Army of the 12 Monkeys to be their prophet, The Witness, a role he adamantly resisted.
In 1959, Athan is conceived by James Cole and Cassandra Railly in the House of Cedar and Pine. Cassie reveals to Cole that she is pregnant on Christmas Day. Unfortunately, soon after this happy moment, Cole meets with Lillian, who explains that he must go back in time and undo the past two years. Cassie's pregnancy continues after the time reset, however, due to the time travel injections that allow for her, James, and the baby, to exist outside of time. Following her abduction to 2163, the Pallid Man reveals to Cassie that she is carrying The Witness.
The newborn Athan is immediately handed over to the custody of the Guardians. In a ritual that takes place in the heart of Titan, Athan is placed in a large chest. The baby is escorted through time to 1921. He is taken to Paris, but the trip is cut short after his trail is picked up by Jennifer, Jones, and his father.
Olivia tells Ramse that James Cole's son is The Witness.
Believing Athan to be The Witness, Ramse travels to 2007 to kill Cassie before she meets Cole and even becomes pregnant. Cole questions Ramse's motives, leading Ramse to tell Cole that The Witness is his own son.
Throughout their pursuit of Athan, James and Cassie continue to struggle with the idea that their son could be The Witness. James blames himself for an evil within Athan.
In 1953, as a young child, Athan is used to indoctrinate members into the cult. Zalmon Shaw, preying on people grieving the losses of family members in tragic accidents, preaches of a timeless Red Forest where they can reunite with their loved ones. These promises draw the earliest members of the Army of the 12 Monkeys. Athan is used to target certain individuals who belong in the 12 Monkeys' ranks. He also murders the remaining event attendees by unleashing a toxic gas before being splintered away by his Guardians.
After returning to his safehouse, Athan is hunted down by the team of time travelers. James can not pull the trigger on his own son. Athan's sole surviving guardian, Sebastian, is able to splinter the two of them to safety before Deacon can finish the job.
In 1879, Athan is a young adult living with Sebastian. Athan is nursed back to health by Sebastian following an accident. Athan is haunted by visions, due to his being Primary. Sebastian urges him to write down what he is seeing. This culminates in the Word of the Witness.
After traveling to countless time periods throughout much of his younger life, including Rome in 1610, Paris in 1840, London in 1940, New York City on September 11, 2001, and 1987 to an unknown location(s), Athan's splinter suit finally breaks, trapping him in 1891. He tasks a blacksmith with replicating a vital component of the suit. In the meantime, Athan meets Eliza. The two fall in love, but Eliza is destined for a tragic death. After repairing his suit, Athan tries 607 times to save her life, but he is unable to do so. Athan has spent much of his life resisting the destiny the Army of the 12 Monkeys has laid out for him, but begins to fall into the allure of a timeless Red Forest, solely to have Eliza back. He is soon confronted by his parents in the church and leads them on a chase through time.
The chase concludes with Athan being captured by his parents in 2017. They take him back to 1959 on December 26th, the day after James erased his life with Cassie. They are pursued by Jones, Hannah, and others. A massive firefight ensues and Athan is shot. He splinters to 2017, where is discovered by Jennifer Goines. Jennifer had seen Athan's body in her visions and set out to save him. Jennifer nurses him back to health. By 2018, Athan determines that he is ready to return to 1959 to save his parents. He tells Jennifer that stopping the 12 Monkeys and saving time is now her mission. Donning the attire of The Witness, Athan splinters into Titan. He kills dozens of Acolytes. After safely getting Cassie and James out of Titan, he is captured by the Army of the 12 Monkeys. In a confrontation with Olivia, he reveals to her that he is not, in fact, The Witness. That title, he realizes, falls to her. In her rage, Olivia murders him.
- "Memory of Tomorrow" (mentioned only)
- "Enemy" (mentioned only)
- "Causality" (mentioned only)