<Li> Anna Kolcheck (girlfriend) </Li> <Tr> <Th> Nationality </Th> <Td> American </Td> </Tr> <P> G. Callen (born: Grisha Alekandrovich 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)". </P> <P> 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 . </P>

What does the g stand for in agent g callen