Committed various crimes while working for and running the Jerome organization [1988-1990]
Kidnapped and murdered his sister Olivia 
Killed Johnathon Paget during a gunfight 
Operated an online gambling ring and knowingly lured Morgan Corinthos into gambling debt [revealed Aug 2, 2013]
Shot Vince, a henchman within his organization, and left him to die in the harbor [Sept 16, 2013]
Ordered Carlos Rivera to destroy a shipment that belonged to Sonny Corinthos [Sep 18, 2013]
Ordered his henchmen to ransack the Corinthos coffee warehouse [revealed Oct 23, 2013]
Ordered Carlos Rivera to kill Morgan Corinthos [Oct 28, 2013]
Imported and distributed illegal drugs [Apr-May 2014]
Arrested for drug trafficking [May 21, 2014]
Shot Mickey Diamond [Jul 29, 2014]
Arrested on charges of fraud and conspiracy to aid in the wrongful imprisonment of Luke Spencer [Dec 3, 2014]
Ordered Carlos Rivera to kidnap Ric Lansing and hold him in the trunk of a car [Dec 18, 2014]
Escaped from prison [Jan 29, 2015]
Shot Johnny Zacchara in the shoulder [Feb 3, 2015]
Julian Jerome, the son of notorious crime figure Victor Jerome, desired to take his father's place at the helm of the family business. Julian believed he had secured his spot as his father's successor but his sister Olivia disagreed. She also had her sights set on running the family business and made an unsuccessful attempt at killing Julian. However, Julian was on to his sister and with their father's help they faked Julian's death. Victor died soon after which left Julian alone to deal with his sister. He eventually used Olivia's obsession with Duke Lavery, a member of the family's organization, to set her up for Duke's murder. When Olivia figured out Julian's plan, he killed her.
After Olivia's death, Julian was the sole boss of the family but he was concerned with a man named Jonathon Paget, although the man claimed to be Duke Lavery, a man who was believed to be deceased. Jonathon and Julian engaged in a shoot-out and were both presumed deceased. After Julian was believed to be killed, his lover Cheryl Stansbury was revealed to be pregnant with his child. She gave birth to a son and he was adopted and raised by Tony Jones and Bobbie Spencer.
The Jerome family was not heard of again until several years later. Julian's sister Ava and her daughter Kiki took up residence in Port Charles. Julian arrived shortly after using the name Derek Wells. He and Ava discussed how they planned to take over the territory which used to belong to the Jerome family. The territory was currently held by Sonny Corinthos and Ava used their online gambling ring to connect Sonny's son with her daughter. Julian was pleased to learn that Kiki and Morgan were engaged but reminded his sister that she needed to gain access to ELQ as well. In the meantime, Julian went after Sonny's girlfriend, Connie Falconeri, by asserting his power as owner of the Port Charles Press, which included Crimson magazine.
While using the alias Derek Wells, Julian met Alexis Davis and her daughter Sam Morgan. Sam's son required a bone marrow transplant and Julian was a match. He agreed to be a donor and learned that Alexis could not contact Sam's father because Sam had been the product of a one-night stand while Alexis was a teenager. When Alexis spoke about the night she had become pregnant, Julian realized that he was Sam's father. Afterwards he contemplated if he should reveal his connection to Sam and Danny.
Meanwhile, Julian and Ava continued to plot Sonny's demise but feared they had lost the element of surprise after one of their henchmen was captured by Sonny's organization. However, the man revealed that he worked for Julian Jerome, not Derek Wells, and Sonny remained unaware of the presence of the rival mob family. Julian and Ava stepped up their efforts and started to attack Sonny's business. As Sonny pondered the identity of his new rival, Ava's former son-in-law and lover, Morgan Corinthos, overheard a conversation in which Julian revealed his identity. Julian planned to have Morgan killed before he could share the knowledge with his father Sonny. However, Morgan vowed to keep silent and promised to help Julian take down Sonny.
With Morgan's assistance, Julian learned that Sonny knew his real identity and planned to have him killed outside of Ava's art gallery after Franco's show. When Sonny confronted him at the gallery, Julian admitted his true identity and apologized for his deception to both Sam and Alexis. Julian reminded everyone that he had saved his grandson's life by donating bone marrow and that Danny could suffer in the future if the cancer returned and Julian was no longer alive to serve as his donor. Sam begged Sonny to spare Julian's life for Danny's sake and he agreed but challenged Julian to bank his bone marrow instead of hiding behind a child. Sam begged Julian to prove he cared for her and Danny as more than a bargaining chip against Sonny but he refused to make and advanced donation. Alexis also tried to convince Julian on Sam's behalf but he silenced her with a kiss.
Although Julian continued to use Sam's son for protection, he repeatedly reached out to his daughter and asked her for the chance to get to know him. As he slowly made inroads with Sam, he learned that he also had a son named Lucas Jones. He was thrilled to meet Lucas but was taken aback after his son revealed that he was gay. Julian did not initially handle the news well and turned to Alexis for parenting advice.
As Julian's family grew, his relationship with Ava became more strained. The siblings kept secrets from one another and each developed separate alliances outside of the family. Ava aligned herself with Sonny while Julian continued to take orders from Luke Spencer. Meanwhile, Julian explored a personal relationship with Alexis and his children allowed him to be a part of their lives. With Alexis and his family in mind, Julian decided to leave organized crime and notified Luke of his decision. Luke reminded Julian that mob business was a lifetime commitment and sent his message via a bullet into Lucas' chest.
Lucas survived but Julian realized that he could not leave the mob. Instead he allowed Alexis to believe that he was out of the business and falsely claimed that her ex-husband Ric had been his boss. Julian continued to lie to Alexis after he received another warning from Luke in the form of a fire at her house. No one was harmed but Julian tried to distance himself from Alexis to keep her safe. However, he was unable to stay away and declared his love for her.
When Alexis grew tired of Julian's dishonesty, she placed their relationship on hold. Julian sensed that she was serious and confessed that he had falsely framed Ric to protect his real boss, Luke Spencer. Alexis was horrified by the secrets that Julian had kept and he hoped that she would understand that he had done what was necessary to protect his family. When Julian realized that Alexis was unable to forgive him, he became more entrenched in organized crime. He formed an alliance with Johnny Zacchara and continued to work for Luke.
Julian was ordered to kill Jordan but he chose not to carry out the order after Jordan announced that she was under the protection of the Corinthos organization. Julian chose to let Jordan live in order to avoid a mob war. Luke did not agree with the decision and ordered a hit on Julian to be carried out by Carlos. When Carlos held Julian at gunpoint, the men decided their best course of action against their formidable boss was for Julian to seek refuge at Pentonville. He falsely confessed to the murder of Anthony Zacchara and joined his enemy, Sonny, in prison.
While in Pentonville, Julian and Sonny joined forces against Johnny and Luke after Luke continued to threaten their families. Julian and Sonny escaped from prison with Ava and Franco and raced to save their loved ones. However, Johnny and Carlos tracked them down and a shoot-out ensued. Julian was shot in the leg and hospitalized. As he recovered, he learned that Sonny had saved Lucas and many others from Luke's most recent threat. Although Julian was thrilled to learn that his son was safe, his joy was tempered by the news that Ava was presumed deceased after Carlos had shot her in the chest. Alexis personally informed Julian about his sister and Julian and Alexis reconciled. Alexis arranged for the charges to be dropped against Julian and she ended her relationship with Ned.
Shortly after Julian and Alexis reunited, Julian learned that Olivia Falconeri was pregnant and he wondered if the child was a product of the one night he and Olivia had spent together. Olivia vehemently denied any possibility that Julian had fathered her child but Julian remained suspicious even after Ned claimed that he was unborn child's father. When Olivia gave birth prematurely, Julian discovered that the child was his. Julian's elation over his new son was short-lived when he was informed that the child did not survive.