Just like Leroy Jethro Gibbs who runs the Major Case Response Team in Washington D.C, Callen is the also the lead Agent of the Office of Special Projects with his partner being former Navy SEAL, Sam Hanna.
His legal name is G. Callen; when asked what the letter 'G' stands for, he said that no one ever told him because his parents left him when he was a kid and all he has ever found out is that it started with 'G'. Callen learned to speak Russian at age fourteen from his foster sister Alina Rostov during the time Callen lived with her family as an adolescent.
In Season 3 of NCIS Los Angeles, it was revealed that Callen's grandfather was an OSS agent stationed in Romania who killed several members of the Comescu family. The syndicate retaliated, killing Callen's grandfather. Callen's Grandmother - described as "a local Roma girl" - and her child (Callen's Mother) escaped to America.
The Comescu family had not forgotten their grudge, and came looking for the Callens. One of Callen's most vivid memories of his childhood was of being given a toy soldier by a stranger while he played on the beach. He realized that the beach is not in California as he had always assumed, but on the Black Sea coast, and that the toy was given to him to distract him while a Comescu assassin killed his mother.
Callen later learnt that Henrietta Lange had failed to protect his mother. She then gave him his mother's name: Clara. She also told him that his mother was a CIA agent and that she had been her handler when she had gone back on assignment to Romania.
After a year of missions, Clara vanished for six years and resurfaced with two children, desperate to get out of Romania. Hetty had been sent to meet her on the beach where the Comescus killed her. She also said that she doesn't know how he and his sister came to the US and that she had no idea who his father is but that she was the one responsible for getting him out of the orphanage and into foster homes.
Special Agent Callen's career with NCIS has included assignments in Serbia and Russia. On two separate occasions Callen's life was saved by Leroy Jethro Gibbs, once in Serbia and once in Russia.
At the conclusion of Legend Part 2 (episode), Callen was wounded in a drive-by shooting Sam witnessed. The motive for the shooting has not been disclosed, however the Russian woman next to his apartment is seen to have left immediately after his shooting, smiling.
Ironically just seconds before being shot, Callen had remarked to Hanna that he thought it was time for him to move again, and that he felt as though he was being watched.
Four months later Callen returned to his duties.
The case was closed when it was revealed that a former CIA operative Ethan Stanhope arranged the assassination attempt. Stanhope desired to eliminate all persons with knowledge of Operation Cossack a joint NCIS/CIA operation in Russia that failed when it was compromised by Stanhope. Stanhope's goal was to conceal his treasonous actions and prevent any adverse disclosures that would have harmed his business ventures.
Relationships with Colleagues
Leroy Jethro Gibbs
While on a mission in Serbia, Gibbs saved Callen's life. Gibbs also asserted that he saved Callen's life in Russia as well, which Callen denies. Callen has an intimate knowledge of Gibbs' past since he is aware of Gibbs's boat building hobby, as well as being aware of his three failed marriages. It is interesting that Gibbs in episode Legend Part 1 (episode) told Callen that he had been married four times, a fact Gibbs tends to keep close to the vest. Callen is one of five people who call Gibbs "Jethro." He gives McGee a sniper's magazine to use for conversation with Gibbs on their return flight to D.C., saying it worked for him. Callen by his own admission considers Gibbs family.
Callen also seems particularly close with his current partner, Sam Hanna. At least once in most episodes, Hanna displays mother-hen-like concern for Callen (often directed at risks he takes or his neglecting his own needs). When reflecting on a previous experience as a SEAL, he confessed to Callen "I can't lose another partner." Callen also seems to know more about Hanna's personal life than the others, including the fact that Hanna has two mentioned children.
- Callen is played by Chris O'Donnell who viewers may recognize from his role as Robin in "Batman and Robin" and "Batman Forever".
- In the first two seasons of NCIS: Los Angeles, Callen and his colleagues with the exception of Detective Marty Deeks carried a SIG-Sauer P228, the current weapon of choice for their Washington D.C counterparts, the Major Case Response Team led by Leroy Jethro Gibbs. At the beginning of Season 3, however, they switched to the new model SIG-Sauer P229 with the redesigned slide and new grips which they have continued to carry to this day.
- With the exception of JAG, Callen is the only NCIS: Los Angeles character along with Sam Hanna and Kensi Blye to have appeared on NCIS and Hawaii Five-0.
- Chris O'Donnell was mentioned in the Season 6 episode South by Southwest (episode) by Anthony DiNozzo in regards to his role in the 1992 film, "Scent of a Woman".
- NCIS: (6 season; 3 episodes; First appearance)
- NCIS: Los Angeles (See G. Callen on the NCIS: Los Angeles Database for more details)
- Hawaii Five-0: Episode:Pa Make Loa (Hawaii Five-0)