He was born and raised in Brooklyn, New York. His dream as a child was to become a Navy Seal, a goal that he achieved.
Sam has a sense of honor for other people who serve for their country. From the outside, he seems tough, and is usually harsh to suspects who don't follow the rules; on the inside, he has a big heart, loves his family, and is very emotional when it comes to people who are close to him. He always has the protector instinct; Nate Getz once revealed that Sam's biggest weakness is his need to protect everyone around him.
Prior to joining NCIS, Special Agent Hanna served as member of the United States Navy SEALs. During his service in the SEALs, Special Agent Hanna had dealings with the Kidon unit of Mossad. While in the Navy, Sam served in Bosnia, Afghanistan, and Iraq. While on a mission in Bosnia, Sam and another member of his squad Dickerson were captured and tortured before being buried alive. Prior to his burial Dickerson was shot and died of his wound during captivity. Sam was ultimately rescued by other members of the team.
Sam joined NCIS after leaving the military. His current partner is G. Callen. During the joint operation run with Special Agent Leroy Jethro Gibbs's team, Sam served as Callen's backup. He witnessed the shooting of Callen at the conclusion of NCIS Legend (Part 2), returning fire at the assassins as they sped away and was on the scene seconds after Callen was hit. He was seen cradling Callen in his arms while calling for an ambulance.
In the aftermath of the attack on Callen, Sam assisted Agent Macy in the interrogation of the surviving terrorist, Haziq Khaleel, in order to determine whether or not the cell was connected to the assassination attempt on Callen. In the episode LD50, Callen said that if asked if a glass was half-empty or half-full, Sam would see it as half-full.
Also, as a result of Callen being arrested for killing The Chameleon, Sam has been promoted from Senior Agent to Special Agent in charge of the Office of Special Projects team although it was later revealed that the Chameleon's death was faked and Callen and Henrietta Lange later returned to their respective positions.
During his time as a Seal an Afghani elder helped him when he was wounded on a mission, which is the plot for the Season 4 episode, Lokhay.
In previous episodes, Sam has mentioned having two children and insinuated that he has a wife. This was previously unknown by the rest of the team, although when Agent Callen was questioned about it, he refused to answer, suggesting that he knew whether Sam's claim was true or not. Callen confirmed that Sam has a family during the concluding moments of Honor, when Hetty asked him where Agent Hanna was and he replied, "Agent Hanna had gone home to see his family." At the end of Betrayal, Sam is shown coming home at night and checking in on his daughter before joining his wife in bed. It is also suggested that despite his wife's knowledge that Sam is a government agent, she is not privy to the details or the extent of Sam's actions whenever he is undercover.
In Season Four the series dropped a bombshell when it was revealed Sam’s wife, Michelle Hanna, was an undercover agent in Sidorov’s crew who is now back undercover after what appears to be a period of time away from the CIA. Michelle felt that being in the CIA was a part of who she was.
- Sam has been known to speak and understand Spanish, Japanese, Arabic and Farsi. He also has an encyclopedic knowledge of the Qua'ran, although it is unknown what, if any, religious beliefs he holds. Because of his knowledge of Islam and Arabic, his undercover assignments often pertain to Islamic extremist groups, both in America and overseas in the Middle East and Africa.
- He revealed he owns a bomb shelter as revealed in Episode:Blye, K..
- He is friends with Steve McGarrett from Hawaii Five-0, who is also a SEAL, this implies that Sam met McGarrett during his Navy service.
- G.Callen and Henrietta Lange are the only one who knows about his past and family, and the only members of the team he trusts.
- G.Callen is the "Uncle" of his daughter as revealed in Episode:Higher Power.
- He played Football in High school as a Wide Receiver.
- He is very proud of his time as a SEAL, which can be analogous to NCIS Agent Leroy Jethro Gibbs's own history as a Marine.
- He owned a 1970 Dodge Challenger that had been bought by his father the year it was released and worked on it as a restoration project when his work became too stressful. He was deeply upset when said car was stolen but never found out that it had been stripped and torched as Eric Beale and Nell Jones who had found the car vowed to keep it a secret from them.
- He has been obsessed with origami and has steadily improved his skill at origami since Episode:Search and Destroy , where Callen and Hetty identified his crane as a duck.
- In Episode: Vengeance, he is referred to as Chief Hanna, indicating his rank in the SEALs was most likely Chief Petty Officer (E-7)
- Near the end of Episode 12 Season 4, It shows Sam in full dress uniform and his rank is that of a Senior Chief Petty Officer (E-8)
- He and Callen have been partners for more than 5 years.
- Like Special Agent Timothy McGee, Sam is afraid of maggots as revealed in Episode:Brimstone. He and McGee are also left-handed although he was seen writing with his right hand.
- Sam's wife and the mother of his daughter is Michelle, a woman he met while both were working on a CIA taskforce. This is possibly the reason why his family has remained such a secret from the world. Only a select few know his wife's true identity, including Callen, Henrietta Lange.
- The details of Sam's past were revealed to Assistant Director Owen Granger by Henrietta Lange and to Kensi and Deeks by Callen. Episode:Rude Awakenings.
- He has Coulrophobia (fear of Clowns) and hates Snakes.
- Sam is the only member of the team who is married and has children.