He played a large role in the concluding episodes of Season 8 of NCIS, and was eventually killed by Agent Gibbs and Director Vance in the latter-half of Pyramid (episode), finally ending his rampage for good.
Originally a US sailor, Cobb was one of the few who was hired by the CIA as part of an operation code-named Operation Frankenstein, in which Director Vance supposedly had a part as well. The operation involved recruiting US sailors to be part of a behavior modification program which would lead to them being able to remain calm and composed in the worst and most extreme of circumstances.
The CIA would then use them as assassins on various sides of the globe, using their cover as Navy sailors. Cobb passed the training and was sent on a first mission to kill an Al-Qaeda operative in an unnamed location. He completed the task successfully but the strain of his training and the trauma of taking a human life left him forever changed.
Upon returning to the program, the CIA realized that he had broken, as Cobb believed he no longer had to obey any kind of authority, and decided to send him back to his unit with half a dozen passports with different identities.
Cobb later disappeared, resurfacing in Rota, Spain, where he targeted an enlisted man who came to port, marking the beginning of his killing spree. He later killed in different locations such as Japan, Guam and Norfolk before heading to Washington. There, he was met by Gibbs's team and also EJ Barrett's team who had been hunting him since Rota. Cobb was able to keep ahead of them and out of their reach.
He then headed to Hawaii where Barrett and her team followed him. He tried to kill another sailor but Kort intervened, losing his left eye in the process with Kort later delivering this eye to Anthony DiNozzo and Ziva David through a drink in a bar.
The CIA had identified Cobb as the Port to Port Killer and had been trying to stop him. Kort claims that the only reason that NCIS hadn't been informed was because it was their mess and they wanted to clean it up.
Cobb began observing Barrett's team in great detail and even infiltrated the Navy Yard to watch them, all the while setting a trap for them. He killed an NCIS agent and stole his access card and arranged for himself to be seen on a security camera. A few hours later, during an intense storm, he killed Michael Franks as the latter was walking out of Gibbs's house but not before Franks managed to shot Cobb in the leg, wounding Cobb but Cobb fled before Gibbs got outside.
Gibbs later figured out that Cobb sympathized with Gibbs for being put below Barrett, a similar situation to what Cobb felt, he saw this for himself in the Navy Yard and acted, even though Gibbs realized that Cobb was in his house before killing Gibbs's mentor.
He later ambushed Barrett's team as they were searching the building he had arranged for them to find. He killed Agent Gayne Levin (his last murder victim) in the resulting fire fight, wounded Agent Simon Cade severely (although Cade later made a few recovery), and struggled briefly with Agent Erica Jane Barrett until he managed to overpower her and place a gun to her throat.
He wrapped her in plastic wrap and placed her in the trunk of her car, keying in a phone number on the side of the car before leaving (the number belonging to Ziva David's newest boyfriend), Ray Cruz.
After trapping Ziva and moving her elsewhere, Cobb strangely gave himself up to NCIS without a fight, though he was not done yet. In the resulting interrogation, he ominously relayed to Gibbs a story of a young boy (Cobb) and his horse, who was near death. The boy called his father, a Navy Captain, who, in order to "teach a proper lesson" to his son, did not call a vet to order euthanasia, but instead shot the horse point-blank to "end its misery." Gibbs then asked Cobb if he'd like him to end his misery.
Following the story as a lead, Gibbs went to Abigail Sciuto who found traces of certain lineaments on Cobb's pants, lineaments which could be used to sooth aching joints in animals. Gibbs located the abandoned barn which used to be Cobb's, and discovered a cymbal-playing monkey at the scene, along with a silenced but alive Ziva. She immediately warned the crew that she was a diversion so that Cobb could get free.
Back at NCIS HQ and while being escorted to lock-up, Cobb broke free of his restraints, attacking the NCIS agent guarding him before taking EJ and Palmer hostage while forcing the two out of the building.
Gibbs, Vance, and SECNAV Davenport were in pursuit, figuring, correctly, that the Port to Port Killer would likely return to where his ordeal began--the building in which Project Frankenstein was conducted--and soon discovered him there, "training" three masked individuals Kort, Palmer, and EJ by spraying them with a water hose.
After a brief encounter with the SECNAV, Cobb unmasked his victims, knocked out Kort with his own gun, and hoheld EJ by the throat, gun pointed at her.
Davenport who had arrived first told Cobb that they could speak about it but Cobb later figured out that Davenport wasn't alone, forcing Gibbs and Vance to emerge and back him Davenport shortly while telling Cobb to surrender. SECNAV told the Port to Port Killer that he wanted to help him but Cobb didn't believe Davenport and instead lunged forward, intending to shoot Davenport.
Thankfully, at Gibbs's signal, Palmer and EJ ducked for cover, giving Gibbs and Vance an opportunity to shoot at Cobb which they did, the sheer force of gunfire causing Cobb to fall out of a window and crash onto a sedan, setting off many alarms and as it closed up on his face, it was shown that Cobb had died with a smile on his face.
- Retired Navy Captain Nathan Finney- (throat slit).
- Captain Douglas Johnson- (Rota Victim, throat slit).
- Seamen Apprentice Steven Bennett- (Japan Victim, throat slit).
- Rear Admiral Arthur Reed- (Guam Victim, throat Slit).
- Seaman Derek Balfour- (Norfolk Victim, throat slit).
- NCIS Special Agent Earl Stark- (Throat slit, used ID to enter NCIS many times).
- Michael Franks (stabbed, stole his firearm).
- Gayne Levin- (shot, later bled to death from his injuries).
- Sergeant Kevin Jericho- (Hawaii Victim).
- Erica Jane Barrett- (twice).
- Simon Cade- (shot, survived his injuries).
- Trent Kort- (twice attempted, failed).
- James Palmer- (kidnapped, tortured, attempted to kill, failed).
- Phillip Davenport- (attempted, failed).
- Unnamed NCIS Agent- (attacked, survived with only a broken nose and a concussion).