Harper Dearing was the CEO of Dorado Hills Investments, a multinational venture capital group that specializes in technology companies. After the death of his son, Evan, Dearing went insane and later became the leader of a terrorist cell taking advantage of the weakness in the wiring of certain Navy Ships to firebomb them while swearing revenge against the Navy and NCIS, both of whom he blamed for his son's death.
Dearing launched an attack against the Navy Yard which left the building in ruins and numerous unnamed employees dead while leaving the survivors deeply traumatized. However, his reign of terror finally ended in May 2012 when Leroy Jethro Gibbs, the leader of the NCIS Major Case Response Team tracked Dearing down and after a long talk, stabbed the other man with a knife, finally ending Dearing's rampage for good.
In the Season 9 episode, Up in Smoke (episode), Dr. Samantha Ryan describes Dearing as being a "sociopathic, paranoid narcissist".
Dearing once had a happy life and marriage and was proud when his young son, Evan joined the Navy as a sailor. However, Evan and two other NCIS members played a practical joke on one of the members of NCIS by videotaping the member in question having sex and then showing it to the other members of the Navy. This resulted in Evan being reassigned to another ship.
However, Evan was killed from the destruction of the vessel he was on due to faulty hulls on the Navy Ships, and the fleet wasn't entirely updated completely due to the events of 9/11. Evan's death turned Dearing for the worst as he began getting into DUIs and other disturbing behavior that eventually led to his and his wife getting a divorce.
Unable to cope with Evan's death, Dearing eventually became a terrorist hellbent on exacting revenge against both the Navy and NCIS who he blamed for sending his son, Evan to his death. He embarked on a long campaign, leaving nothing but a trail of carnage, destruction and death in his wake.
Having learned of Project: Aquamarine and its connection to vessels in the United States Navy from Levine's Watcher microchip, which Jonathan Cole and Sean Latham auctioned off earlier to him, he hired arsonist Bruce Johnson to locate Carter Plimpton at the Equinox Warehouse and interrogate him for the Aquamarine file, kill him, and steal the Aquamarine file, and presumably to lure NCIS agent Anthony DiNozzo and BPD Arson detective Jason King into a death trap on board a cargo ship that was the victim of an arson attack.
Eventually, he either directly killed Bruce Johnson with an incendiary car bomb or had him killed via that method, having anticipated the likelihood that Bruce Johnson would try to invoke a plea bargain with NCIS exposing his identity in exchange for a lighter sentence.
Likewise, armed with the information of two-thirds of the Navy not having updated the wiring system to remove the faulty wiring developed by Equinox, he sent various arson-terrorists to blow up the U.S.S. Brewster and the U.S.S. Benjamin Franklin to test the weaknesses in the ships.
Although the former partially succeeded in causing some major damage to the ship (having failed to cause more damage in part because of it igniting propane tanks and drowning out the explosion's potency before it could affect the ammunition chamber below), the latter had failed due to the efforts of NCIS agents Stanley Burley, Ziva David, and DiNozzo, with the arson terrorist responsible eventually revealing his identity (or rather, key leads to his identity) in the hopes of avoiding transfer to Gitmo prison.
They eventually confirmed the DNA match on some of the documents, although they discovered that even though he is the CEO of the company, he hadn't even been seen inside of the company for a year. Gibbs then issued a manhunt for Dearing for his terrorist activities, making him the first top threat to American soil since the late Osama bin Laden of al Qaida.
Afterwards, he had a dentist, Dr. Jay Berman, insert a fake tooth containing a bug of his design into Probationary Agent Ned Dorneget, which was discovered a day later. After Jay Sherman was exposed, he attempted to lie about his involvement with Dearing, although he ended up revealing everything he knew upon Dearing's command when he contacted NCIS directly. He then appeared in a Naval Yard, as well as hid a model boat in the bushes before leaving, in order for NCIS to know he was there.
He then implanted the watcher microchip with a list of data (actually a fake list of supplies that the acting president of Dorado was using for embezzlement purposes), and then had the ex-policeman spotted by NCIS and killed as he was bargaining for a plea-bargain to send NCIS on a wild goose chase regarding the seeming development of defective Artillery Shells that would blow up the ship, sent an anonymous tip to NCIS about embezzlement, and deliberately let himself talk to Gibbs long enough to find the location of the supposed warehouse that the makeshift factory was being made at, placing the Navy on high alert and cancelling any and all Naval Training exercises until the threat can be removed, resulting in Vance arriving from NATO to talk with the Navy Brass.
After it was discovered that it was a wild goose chase, it was later revealed that Vance had disappeared at the airport. Dearing had him abducted, apparently using that wild goose chase to lure Vance into his range. However, he wasn't trying to target Vance specifically. Rather, he was trying to get his SUV so he could then rig the seating as an explosive device with several M112 Charges and a cellphone detonator so Vance, upon being rescued, unknowingly deliver a car-bomb to the NCIS compound.
Dearing later blew up Blake Larson's house for his part in sending his son to the doomed vessel that resulted in his death just as the MCRT team arrived to try and find him, as well as left a message for Gibbs, specifically. He also contacted Dr. Samantha Ryan and commented on her son being nearby with the strong implication that he would abduct him should she not stay off his trail. Eventually, having somehow deduced who Ryan's ex-husband was and his incarceration, he bribed the judge into having her husband released due to a "technicality" as a means to intimidate Ryan into fleeing with her son and thus render her incapable of being of any aid for NCIS.
He also anticipated the likelihood that NCIS would attempt to recruit Jonathan Cole as a double agent to get a bead on him, so he instead arranged for a waitress to deliver to Cole a cell phone to maintain contact, and also relay his real reason for abducting Vance, which he ambiguously stated as "justice." He later succeeded in blowing up Vance's car, resulting in damage to the NCIS building, Cole's death, and an unspecified amount of casualties while leaving the Navy Yard in a state of destruction and its employees, including members of the NCIS Major Case Response Team were left traumatized by the attack.
As season 10 started, Dearing watched the footage and was then coaxed into a motel by Lorraine. Lorraine, however, turned out to be a FBI agent, and she, alongside a FBI contingent team, attempted to gun him down while he was in the bathroom. However, he anticipated this likelihood and managed to escape with an explosion in his bag that had been left in the bathroom later going off, resulting in the deaths of Lorraine and the FBI team while leaving the FBI agent, Tobias Fornell who had joined the search for Dearing more hellbent on revenge than ever.
He later made a video conference call to agent Gibbs in MTAC. As Agent McGee managed to trace Dearing's location via his call, agents were immediately deployed to an empty car parking lot on the orders of SECNAV Clayton Jarvis. It was seen there that Dearing detonated a bomb blowing the car and what it seemed like himself in the car.
Despite everyone believing Dearing was dead and that the manhunt was over, Gibbs's uneasy feeling about this continued, prompting him to call in Dr. Donald Mallard who had been on leave since suffering a heart attack just mere seconds after learning of the Navy Yard bombing. Thanks to Ducky, Gibbs's suspicions were confirmed: Harper was still alive and that the remains found at the scene belonged to his brother, Lawrence who had died of a heart attack. In addition, he also forced his sister to lie for him to the NCIS about his fate, until his sister, upon being interrogated, reported to the NCIS his last known coordinates.
Unfortunately, by the time the NCIS managed to get to those coordinates, a cabin in the woods, he anticipated their arrival and had long escaped via a rum-smuggling tunnel located underneath the house in a trick door.
After Vance gave him permission, Gibbs headed alone to Harper's house where Evan Dearing had been born and spotted Dearing by a coffee machine trying to serve Gibbs' some coffee.
Due to a malfunction of the coffee machine, he was unable to. Harper walked towards a window, where Gibbs spotted a gun. While this happened, Dearing spoke to Gibbs, stating that they were similar given how like Dearing, Gibbs had suffered the loss of a child.
In the end, Harper reached for his gun and turned around, intending to shoot Gibbs but was shocked when Gibbs, having known what Dearing would do, stabbed the other man right into his heart with his knife with Dearing dying seconds later and finally ending the terrorist's rampage for good.
- The following were involved in the Cargo ship bombing:
- Bruce Johnson- (Killed with a car bomb when he started the ignition and switched it off).
- Fredrick Fountain- (Killed with a single shot to the chest to send NCIS on a wild goose chase).
- Leon Vance - (Abducted from the airport; survived)
- Blake Larson - (Blown up in his own house in revenge for sending his son to the ship that he was killed on)
- Dr. Samantha Ryan- (Forced her and her son to go into hiding after bribing a judge into releasing her ex-husband, a well known felon, under a technicality)
- The NCIS bombing (one known fatality):
- Jonathan Cole- (Killed in the explosion triggered by Dearing)
- The hotel bombing (five fatalities):
- Four unnamed FBI agents
- Leroy Jethro Gibbs- (attempted to shoot but Gibbs killed him first).
- Carter Plimpton- (Hired Bruce Johnson to interrogate him and later to kill him).
- The following were killed in the U.S.S. Brewer bombing:
- Stanley Burley- (Andre Fullerton attempted to kill him while trying to set a bomb on the Benjamin Franklin).
- Ned Dorneget- (Was implanted with a fake tooth that contained a listening device by Dr. Jay Berman, under Dearing's orders).