Kullens as a councilman was shadowed by Susan Williams for a profile, by doing so she followed him to a meeting with Mayor Oliver Queen. Once they got down to business, the councilman acknowledged that Oliver's plans would only benefit "crony capitalists", such as Queen Consolidated some decades before. Oliver later found proof that Kullens was one of those "crony capitalists" since he only voted against Oliver's plans to protect an investment he made that he would have granted him a lot of money. Oliver promised to reveal this information to Susan unless Kullens voted in favor of his plans and Kullens reluctantly agreed to it.
When Adrian Chase anonymously exposed the fact that Oliver covered up the fact that the Green Arrow was responsible for the death of Billy Malone, Kullens ordered a hearing to be held and refused to give Oliver a chance to speak. Thea Queen contemplated blackmailing Kullens with evidence that he covered up the circumstances behind the death of his late wife only for Oliver to refuse. Oliver would later speak publicly to confess to having covered up the circumstances behind Malone's death in order to give the Green Arrow the benefit of doubt as the Green Arrow was giving Star City hope. Kullens was forced to vote against the impeachment.
When it turned out that the district attorney Adrian Chase was hidden under the mask of Prometheus, the city council, led by Kullens, started a chase after him with the help of the police. During a town hall meeting, the man intended to notify Interpol, believing the criminal might want to flee the country. However, the mayor felt that this was not the case, noting that the criminal was not finished here yet. Kullens was not going to believe Queen's mere assumptions, for fear for the fate of the city and its inhabitants.
Kullens later became corrupt and joined Ricardo Diaz's criminal organization along with District Attorney Sam Armand and police Captain Kimberly Hill. While Hill and Armand were motivated to join Diaz to protect their loved ones, Kullens was motivated to join out of greed and due to his hostility towards Oliver. Oliver tried to promise protection to Hill and Armand only for the two of them to refuse, prompting Oliver to fire them. Due to this, the two went to news outlets, broadcasting their firing as a ploy by Oliver to obstruct the investigation into him being Green Arrow. Before the preliminary hearings, Kullens promised to ensure Oliver had a fair hearing but secretly drugged him with Vertigo in order to make Oliver act unstable.
When Oliver presented evidence that Hill and Armand were working for Diaz and claimed he got it from the Green Arrow, Kullens accused Oliver of being Green Arrow since that was what Hill and Armand were investigating him for before they got fired. When Oliver denied this, Kullens argued that Oliver enjoyed working with the Green Arrow as he has been in contact with him. Quentin Lance then excused Oliver from the meeting since Oliver was high on Vertigo. Kullens convinced his fellow council members to impeach Oliver as mayor.
After Oliver used a device that Felicity made on his wrist to copy all of Diaz's files (that contain a list of every person under his payroll) and gave it to Samanda Watson; Kullens was arrested along with all the people under Diaz's payroll by the FBI.
A year later, Kullens would later be released from prison due to hiring a team of lawyers to get him out of prison. Kullens made plans to try to become a city councilman again until his plans were foiled by a stranger. One night, when Kullens was sleeping in his bed after after being released from prison, the stranger quietly broke into his room and injected him with a paralytic drug. Kullens awoke in shock and asked the stranger what he wanted before the latter sliced his throat without any response, killing him.
Although Kullens had ruined his own life and reputation when he chose to align himself with Ricardo Diaz, he did not deserve the death that he received from Stanley Dover; shortly after his death, Kullens' killer, Stanley was brought to justice after being subdued by Oliver Queen and re-incarceration in Slabside Maximum Security Prison.
It is very likely that murdering Kullens, as well as Stanley's recent crimes, such as the murder of B. Dunbar and two other victims, and the attempted murder of Dinah Drake, Oliver Queen, Felicity Smoak and William Clayton respectively, has increased Stanley's prison sentence from several years, to life in prison.
Initially, Kullens seems to be an elderly individual who was kind, thoughtful and gentle, but in truth, Kullens was more concerned about making money and his approval ratings rather than the welfare of the citizens of Star City, Kullens developed a grudge against Oliver Queen for blackmailing him into supporting Oliver's plans when Kullens only voted against them to protect an investment he made that would've earned him more money. The relationship between Oliver and Kullens was so tense that Kullens forbade Oliver from testifying at an impeachment hearing when it was discovered that Oliver covered up the circumstances behind Malone's death. Kullens was also hypocritical as he had the SCPD covered up the fact that his wife died in a car crash from drug abuse, which proves Kullens was a very selfish individual whose own thoughts were improving his lifestyle than serving Star City.
Kullens eventually started working for Ricardo Diaz with Sam Armand and Kimberly Hill, Kimberly was motivated to join Diaz since he threatened to kill her family unless she cooperated and Armand needed money to pay for his son's cancer treatments when Armand couldn't afford it. Kullens was only motivated to join Diaz out of greed, Diaz paid Kullens to get Oliver impeached as mayor and Kullens did by drugging Oliver with Vertigo before the hearing in order to make Oliver appear to be unstable. Kullens knew that Oliver fired Armand and Kimberly for their allegiance to Diaz, not for their investigation into him being Green Arrow. Despite of this, Kullens still waved forth accusations of Oliver being the vigilante and pointed out how Oliver enjoyed being in contact with the Green Arrow. Kullens was proven to be a skilled manipulator, as he manipulated the public into believing that Oliver overstepped his authority as mayor in order to protect himself.
These negative traits of Kullens was what eventually led to his deserved/justified incarceration.