Grisha Alexandrovich Nikolaev or G. Callen (G. or Callen to his NCIS colleagues) is an NCIS Special Agent and also a member of the Office of Special Projects in Los Angeles.
Born in Romania to a Russian father, KGB Major Nikita Alexsandr Reznikov and Clara Callen, a half-Roma CIA agent as well as having a sister named Amy, Callen lived a relatively normal life up until the age of five when his mother sought to escape to the United States along with her two children to avoid being targeted by members of the Comescu family who had long sworn since a blood oath to eliminate any and all traces of the Callen family.
Waiting at a beach, young Callen played in the sand and was subsequently distracted by a man handing him a toy soldier while another man, a second member of the Comescu family shot Clara dead in cold blood with Callen suppressing the memory from his subconscious for many years.
Eventually, both young Callen and Amy were taken from Romania and brought to the United States. The two siblings were split up and subsequently placed in different orphanages.
In 1975, at the age of five, Callen withdrew from the orphanage and was placed in the foster care system instead. He did not have an ideal upbringing as he went through over thirty-seven foster homes, presumably experiencing various problems in the foster homes he was in which in turn left him emotionally damaged and unable to trust anyone whatsoever.
Upon turning eighteen, Callen enlisted in the United States Army although his history and what rank he held remain unknown.
After that, Callen joined the CIA, working alongside Trent Kort.
Callen then left the CIA and joined the DEA- Drug Enforcement Agency and then the FBI before choosing to join NCIS.
After becoming an NCIS Special Agent, Callen befriended and met fellow NCIS Agent Leroy Jethro Gibbs with two assignments bringing both men to Serbia and Russia with Gibbs saving Callen's life on both occasions in the two countries.
At some point, Callen was reassigned to the Office of Special Projects located in Los Angeles where he remains to this day. He also presumably worked alongside a few partners before working alongside his current partner, Sam Hanna.
NCIS Season 6
Callen made his debut appearance in the NCIS Season 6/NCIS: Los Angeles backdoor pilot episode, "Legend Part 1" where he was seen ignoring a call from his boss, NCIS Special Agent Lara Macy before he spoke to his old friend, fellow NCIS Special Agent Leroy Jethro Gibbs.
The two spoke for a while about the past they had shared together although they were interrupted by a young Russian woman cycling by.
After they had finished, Callen left to go get ready for the second undercover operation he would play a main role in.
NCIS: Los Angeles Season 1
Callen appeared in the NCIS: Los Angeles Season 1 premiere episode, "Identity" where he was first seen in a small room, presumably at a B&B possibly in Venice Beach, remembering the near-fatal shooting.
It was also shown that he had been left with scars, presumably permanent on his back as a result of being shot.
After that, Callen packed up his belongings and headed for the beach where he got two coffees.
Some time later, Callen's partner, NCIS Special Agent Sam Hanna arrived with the two men talking with Sam wondering if Callen was ready to come back with Callen insisting he was.
When Sam questioned him on why he'd left his latest area, Callen had said that it was too noisy, revealing that he had a habit of moving around due to the fact that the accommodation he lived in was not suited to him.
The two then grabbed Callen's respective belongings and left but not before Sam told Callen that the new building they now worked in was "noisy".
A while or so later, the Dodge Challenger arrived at an abandoned building with Callen later being left stunned at the fact that the Office of Special Projects worked inside a building that had been condemned following the Northridge Earthquake in 1994.
NCIS: Los Angeles Season 2
NCIS: Los Angeles Season 3
NCIS: Los Angeles Season 4
NCIS: Los Angeles Season 5
NCIS: Los Angeles Season 6
NCIS: Los Angeles Season 7
In Angels and Daemons (episode), Callen was revealed to be keeping an eye on Joelle given how the OSP team had had their identities leaked last year.
He and Sam also got into an argument over the fact that they had agreed to carpool to work but that Callen had failed to give Sam any notice of arriving into work early.
Callen along with the rest of the Office of Special Projects team later gathered in Ops to discuss the team's latest case: the murder of former Navy Lieutenant Larry Overson who had founded the anti-virus company, "OverGuard" with Callen and Sam heading to investigate the last suspected sighting of Overson's former best friend, former Navy Lieutenant Mark Powell.
The two arrived at the area in Winchester and searched Powell's car but discovered that the boot was a mess much to Callen's own personal disgust, causing him to comment that it resembled Kensi's desk.
They both soon discovered that Powell had fled with his belongings, leaving a smashed cell phone with the SIM card having been removed.
As such, Callen contacted Eric and Nell for further information with both Eric and Nell revealing that security footage taken from the marina showed that Powell had been in the area at the same time that Overson had been murdered, resulting in Powell becoming the first official suspect in the murder investigation.
Callen and Sam later arrived in Ops and learnt from Eric and Nell that Powell had taken a bus and would arrive at the metro station, leading to both NCIS Agents suspecting that Powell could flee to San Diego and then Mexico.
A while later, Callen and Sam headed to the bus stop where Powell was. Callen intercepted Powell with Sam later providing back-up but Powell attempted to flee which he did so by throwing his duffel bag at Sam who caught it.
Despite Powell's efforts, Callen caught up to Powell and arrested him, Callen noting the bruise on the left side of Powell's face with Powell insisting that he wasn't saying anything without his lawyer.
In the main area of the Boatshed, Callen and Sam yet again discussed Joelle but the discussion was interrupted by Wilson Rowe, Powell's lawyer informing the two NCIS agents that they were ready.
In Interrogation, Callen and Sam attempted to learn more information, only for Rowe to stonewall Powell but when Powell insisted that he wanted to come clean regardless of the punishment, Rowe stated that he couldn't be Powell's lawyer anymore and left.
With Rowe gone, Powell informed Callen and Sam of the daemon he and Overson had created during their time at the NSA with Callen voicing his belief that the two men had violated the Espionage Act with Powell stating that was why he was running because he had thought Overson had turned him in.
Powell also stated that he and Overson had met and fought but that he hadn't killed him.
Once the Interrogation had finished, Callen and Sam met with Granger to discuss the daemon and the possibility that foreign intelligence agencies had been attempting to infiltrate American tech companies for years.
Later, in Ops, Callen, Sam, Kensi, Deeks and Nell gathered to compare notes on the case with Nell revealing that Vincent Lee, the new security guard for Flibbit barely existed.
Callen then asked Kensi and Deeks to go interrogate Powell about Rowe and then informed Sam that they needed to go undercover at Flibbit.
Despite Eric volunteering, Hetty agreed with Nell, instead both choosing Callen and Sam and informing the two to be prepared to make the fastest billion in history.
Later, Callen posing as "Curtis Williams" headed to Flibbit where he and Sam who was "Samuel Wright" met the programmers including Austin Chopra.
The two later met Jessica Moore and discussed how they could help Flibbit.
Once the meeting had ended, Callen headed off with Chopra with Callen taking the slide down to the bottom level of Flibbit and stating that he'd beaten Chopra.
Callen later spoke with Chopra and discussed the code while Eric told Callen via an earpiece that he'd have to dig a little deeper as Chopra was only showing them the bare minimum.
Once that had ended, Callen and Sam left.
In the Bullpen, the team gathered and learnt that Chopra and Batool Shah were both agents for the ISI- Pakistan Intelligence Service agency and that Batool was presumably responsible for killing Rowe with the team being left stunned when they learnt that the daemon had started uploading to users phones and that Flibbit's users was composed of senators, CEOs and even active members of the United States military.
Later, now wearing NCIS bulletproof vests and carrying guns, Callen, Sam, Kensi and Deeks crept into Flibbit Headquarters and after an intense gunfight, saved Mossad officer Noam Haber who had been posing as the security guard, Vincent Lee and killed Chopra and Shah as well as the third ISI agent: Miles.
Eventually, in the bullpen, Callen and Sam discussed Joelle once again with Callen admitting that he did have some regrets over breaking up with Joelle. He and Sam later left the bullpen, the two engaging in a good old fashioned argument.
Callen is a tall, lean man of muscular build in his early forties with fair skin and also brown hair (originally blonde) and blue eyes.
As an NCIS Special Agent, Callen is trained in the use of firearms, hand-to-hand combat, the processing of evidence and the interrogation of potential suspects.