Played by: Peter KrauseLAFD Captain. Recovering alcoholic with a very dark and troubled past. Dating Athena as of Season 2.
- The Atoner: He was responsible for the apartment fire that killed his family and many other residents. Originally, he intended to kill himself once he'd saved as many people as had died in the fire, but is later convinced out of it.
- Dark and Troubled Past
- A Father to His Men: Deeply involved in taking care of his squad, and even cooks for them.
- The Lost Lenore
- Outliving One's Offspring
- Real Men Cook: He's a very talented chef, much to the appreciation of his unit.
- Token Religious Teammate: Out of his unit, he is the only one with expressed faith, specifically he is a practicing Catholic.
Evan "Buck" Buckley
Played by: Oliver StarkFirefighter. A reckless rookie, but does the job down. Also a huge Casanova.
- Ambiguously Bi: Definitely into women, but his relationship with Eddie is full of chemistry. He also never denies other's loaded comments, from his sister's teasing to an elf complimenting "their" son.
- Character Development: His time with Abby made him more interested in meaningful relationships.
- He also gets more mature even over the course of the first season, while still keeping his hotheadedness. For example, when a crowd of gawkers gathers outside the trailer of a the dead man who used Buck's identity online, Buck demands the coroner take the time to drain the body, allowing the man to pass with some dignity.
- Fire-Forged Friends: With Eddie.
- Hair of Gold, Heart of Gold: Athena calls him this by name.
- Heroic BSoD: After he loses his first patient on the second episode of the first season.
- Hidden Depths: Buck went through SEAL trials before the series started, but dropped out and became a firefighter because he wanted a dangerous, adrenaline-filled job that allowed him to help people instead of harm them. He also tended bar in South America and knows how to deal with tapeworms.
- I Will Wait for You: In the second season, he's determined to keep waiting for Abby to return. He eventually decides to move on during the Halloween episode.
- Ladykiller in Love: Settles down once he begins to fall for Abby, and is hesitant to become intimate out of fear it will ruin things between them.
- Lovable Sex Maniac: Deconstructed. While well-liked by everyone, his antics end up crossing the line into unprofessional and nearly costs him his job. It serves as a wake-up call that he needs to address his problem.
Henrietta "Hen" Wilson
Played by: Aisha HindsFirefighter/Paramedic. Athena's best friend, and lesbian wife with an adopted child.
- Big Beautiful Woman: A heavier-built woman that is treated as desirable and gets love scenes.
- Friend to All Living Things: Very compassionate to any animals they come across, and ensures they're treated as well as their human paitents.
- Mama Bear: Do not threaten her family.
- Twofer Token Minority: She's an African-American lesbian.
Howie "Chimney" Han
Played by: Kenneth ChoiFirefighter/Paramedic. After suffering an accident in episode 3, he's trying to figure out what to do now in his life.
- I Let Gwen Stacy Die: He and his best friend Kevin joined the fire department together. Kevin dies saving a pregnant woman during a fire while Howie is standing a few feet away. Howie is traumatized and feels Survivor Guilt because he could have done what Kevin did but he hesitated so Kevin died instead of him.
- Impaled with Extreme Prejudice: He's impaled through the skull in a car accident, but survives by some miracle.
- Inferiority Superiority Complex: He fears that he isn't as heroic as the others, leading him to make up stories to impress his girlfriend.
- Scars Are Forever: He has a distinct scar on his forehead from his accident.
- Ship Tease: With Maddie. They click as friends almost immediately, and sing bad karaoke together. They start dating.
Played by: Ryan GuzmanA new firefighter introduced in Season 2. A single parent of a young boy.
- Always Someone Better: Buck initially can't stand him, because Eddie seems to be better than him in every way.
- Combat Medic: He served as one, prior to leaving the military.
- Latin Lover: Averted. He's extremely handsome and quickly earns the attention of women, but makes it clear he's not interested. This is because he's still in love with his estranged wife.
- Sex with the Ex: starts sleeping with his estranged wife after he tracks her down.
- Struggling Single Parent: He is raising his son alone, and often struggles to find childcare.
- The War on Terror: He fought in Afghanistan before joining the team.
Played by: Angela BassettLAPD patrol Sergeant. Trying to figure out what best for her family after her husband reveals he's gay.
- Deadpan Snarker: How she handles her job as a cop, and often has to deal with stupid people.
- Mama Bear: She won't tolerate anyone hurting her family, and is willing to use her authority as a police officer to protect them.
- Meaningful Name: She absolutely fits her namesake, the Greek goddess of Wisdom and War.
- Invoked when Hen warns Bobby about Athena's mother.
Played by: Connie Britton911 operator of Season 1. A 42 year old woman trying to take care of her mother. She later befriends and starts dating Buck after he helps in a call during the Pilot.
- Deadpan Snarker: Has her moments, like this comment after her first date with Buck went wrong when he stared choking on bread:Abby: It was all going great till I had to cut a hole in his throat.
- The Dutiful Son: She takes care of her Alzheimer's stricken mother at the expense of herself.
- Put on a Bus: Leaves for Europe at the end of Season 1, following her mother's death.
Played by: Jennifer Love Hewitt.The new main 911 operator as of Season 2. Buck's older sister.
- Dark and Troubled Past: Was married to an abusive husband.
- Domestic Abuse: She moved to LA to get away from her abusive husband, who had promised to kill her when she left him.
- Properly Paranoid: She is utterly terrified that her husband will break into her new apartment and kill her to the point she can't sleep some nights. And what's worst, he's finally found out where she's living now.
- Ship Tease: She has a crush on Chimney. they get together
- Shrinking Violet: She is a trained nurse, but didn't want to work with people when she came to LA. Somewhat justified, since she doesn't want to deal with her abusive husband.