Aiden was conceived when Elizabeth Webber was married to Lucky Spencer. However, the marriage had been rocky, and she'd had an affair with Lucky's brother, Nikolas Cassadine. Aiden's paternity was in question, and the stress of not knowing who the father was took a toll on Liz. She had a mental breakdown, and she admitted herself to Shadybrook. That didn't stop Helena Cassadine from threatening to take Liz's baby and raise it as a Cassadine. Unbeknownst to anyone, Stavros had been clinging to life, and Helena hoped that the news of a new Cassadine heir would give him the will to live.

On July 19, 2010, Aiden was born a month premature, and he was promptly kidnaped from the hospital by a homicidal artist known as Franco. Dante and Jason helped Lucky track Franco down. Aiden was found in the care of Franco's mother. Two DNA tests revealed Aiden to be Nikolas' son, so Liz and Nikolas named him Aiden Alexi Nikolosovich Cassadine.

In early March 2011, Liz began to question Aiden's paternity when Monica saw pictures of the children and remarked how much Aiden looked like Lucky. On March 18, 2011, Liz received the results of a DNA test, but as she started to read them, she noticed that the front door had been left open. To Liz's horror, Jake had run outside, and he had been struck by a hit-and-run driver. Jake was briefly put on life support, but he succumbed to the injuries, and his kidney was donated to Josslyn Jacks.

When Liz finally learned the results of the test, which confirmed her suspicion that Lucky was indeed the father of her youngest son, Lucky had moved on, and he had repaired his relationship with Nikolas. Liz feared that the truth would once again drive the brothers apart. However, a heart-to-heart talk with Jason made Liz realize that she had to be honest. Liz went to the courthouse to tell Lucky the truth, but in the end, she couldn't interrupt his wedding to Siobhan.

On June 21, 2011, Liz found Lucky on the Haunted Star, about to destroy his sobriety by taking a drink, so she told him that Aiden was his son. Lucky had been consumed with guilt because he had nearly killed his wife when he had set fire to his childhood home that he had once shared with Liz. Lucky thought that Liz was lying about Aiden, but she reminded him that Helena Cassadine had been in town both times that they had taken paternity tests, and Helena had desperately wanted a Cassadine heir as well as an opportunity to hurt the Spencer family.

Lucky embraced his son, but Nikolas was shattered that Aiden was not his son. Nikolas had spent a year, bonding with the infant, and losing Aiden cut deeply. Nikolas kidnapped Aiden with the intention of raising him on the lam, but in the end, both Liz and Lucky were too important to Nikolas. Nikolas returned his nephew to Lucky and Liz.

In late August 2011, Lucky's wife was murdered, so he decided to carry out her last wishes by taking Siobhan's ashes to Ireland. Lucky realized that his life in Port Charles was over, so he remained in Ireland. Over the years, he stayed in touch with Cameron and Aiden through video calls and letters.

In November 2011, Aiden was diagnosed with idiopathic thrombocytopenic purpura (ITP), and his Aunt Lulu provided Aiden with a life-saving blood transfusion. A few years later, in July 2015, Aiden briefly reunited with his father when Lucky returned home with Aiden's brother Jake. Jake had been kidnapped and held captive on Cassadine Island by Helena Cassadine.

On August 23, 2018, Aiden expressed a desire to get Princess Kalinda-themed school supplies. Aiden was disappointed when Cameron discouraged Aiden's preference for the cartoon princess.

On October 18, 2018, Liz and her fiancé, Franco Baldwin, had a meeting with Aiden's teacher, Willow Tait. Willow expressed concern about Aiden, and how he tended to separate himself from the other children. Liz was shocked because Aiden was a sweet, bright, and helpful child. Willow warned them that Aiden had been the target of bullying, so she encouraged them to talk to Aiden.

Aiden refused to tell his mom that the kids had been calling him "Gayden," but he couldn't keep the secret for long because of online bullying. Soon, Laura figured out what was going on and who had been bullying Aiden. The culprit was Lulu's daughter -- and Aiden's cousin -- Charlotte Cassadine. Charlotte insisted that she had only been trying to help Aiden by pointing out his flaws and that the other children picked on him, too. The adults explained to Charlotte that her criticisms had hurt, and she apologized to Aiden. However, the damage had been done. Aiden continued to be tormented by his classmates.

At home, Franco discovered that Aiden had a love for baking and a knack for creating delicious desserts. Franco encouraged Aiden to pursue his passion, and Aiden's brothers were equally supportive. Liz reached out to Lucas Jones, Brad Cooper, and her childhood friend Terry Randolph for insight as to how to move forward with her son. Everyone around Aiden encouraged his uniqueness, but at school, things remained difficult.

On April 16, 2019, Cameron was suspended from school for getting into a fight with a classmate who had ridiculed Aiden by using homophobic slurs. Cameron defended his brother's honor, but he questioned why Liz couldn't talk to Aiden about acting "a little less gay."