G. Callen (born: Grisha Alexandrovich Nikolaev) is a fictional character in the show NCIS: Los Angeles portrayed by Chris O'Donnell. He is an NCIS Special Agent in Charge, and the senior agent assigned to the Office of Special Projects. O'Donnell made his first appearance during NCIS' sixth season episode Legend (Part 1) . Prior to the series, Callen and Hanna had been partnered together for two years ( Partner ), while he and Lange first met when he escaped from a juvenile detention center, and Hetty kept him from being re-arrested ( Rage ). While his friends address him as G , Lange refuses to do so, saying, It's not a name, it's a letter. She instead addresses him as Mr. Callen ( Identity ). Callen once served with his good friend Leroy Jethro Gibbs, who now works at the NCIS Headquarters located in the Washington Navy Yard. Callen specializes in deep undercover work. In addition to English, Callen is fluent in at least six other languages: Spanish, Polish, Russian, German (with an English accent, which is claimed to be Austrian), Italian (with a Northern accent), and French.[2] Callen also claims to speak Czech and Romanian;[3] furthermore, his Russian is arguably good enough to be taken for one, but not the other, Chechen dialect.[4] That fluency allowed Callen to infiltrate a Chechen terrorist cell in season four episode The Chosen One which eerily presaged the Boston Marathon bombing by Chechen immigrants less than three months later. The fake death certificate shown by Hetty to Alexa Comescu in the season-two finale states that his date of birth is March 11, 1970.[5] In Archangel , Callen states that the first time he fired a gun was at the age of 20. In the same episode, it was revealed that Hetty has beaten him on a race up the NCIS rock wall three times in a row, and Callen refuses to challenge her to a re-match despite goading from Sam Hanna. In the episode Pushback , it is revealed that Callen lived in 37 foster homes starting from the age of five. He sometimes moved every few days, and the longest he ever stayed in one place was for three months at fourteen, when he lived with the family of a Russian girl named Alina Rostoff (whom he called little sister ). It is revealed through flashbacks in the season two finale that Callen spent at least part of his early childhood on the Romanian coast of the Black Sea.[6] It is revealed in Identity that he is called G not because he dislikes his first name, but because he does not actually know what it stands for, as the system never told him. As an adult, his foster-sister Rostoff was secretly sent to watch Callen and to prevent him from being killed by Russian mobsters. Callen is fluent in Russian due to his former relationship with the Rostoff family. Throughout the first season, it is shown that Callen is homeless, staying temporarily with his various NCIS colleagues and sometimes in the Operations Center itself. Prior to joining NCIS, Callen worked for the Drug Enforcement Administration and Central Intelligence Agency. While with the Agency, he worked alongside recurring NCIS character, Trent Kort (David Dayan Fisher), and was partnered with Tracy Rosetti (Marisol Nichols); as part of their undercover mission in Uzbekistan, Callen and Tracy married , using the surname Keller. Following this mission, where Callen accused Tracy of placing the success of the operation above both their professional and personal partnerships, the two 'divorced', with Callen joking that in the settlement Tracy received custody of Buddy, their dog. The marriage and subsequent divorce were of course fake. Show less «