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Alex O'Loughlin as Lieutenant Commander Steve McGarrett, USNR. A decorated former Navy SEAL, Steve McGarrett is head of the Five-0 Task Force and son of retired HPD Sergeant John McGarrett. John's murder and storyline forms the premise of Steve's return to Hawaii and the formation of the Task Force.
Scott Caan as Detective Sergeant Danny Williams. He is a divorced single father who transferred from Newark PD in New Jersey to be with his daughter and is the de facto second-in-command of Five-0.
Daniel Dae Kim as Detective Lieutenant Chin Ho Kelly, (seasons 1–7). A veteran HPD detective, he was John McGarrett's former rookie and provides technical expertise and local know-how. During the season 7 finale, Chin is offered the lead position of the Five-0 Task Force established in San Francisco, which he later accepts. This was written into the show after Kim departed the series in late June 2017 prior to the start of production of the eighth season due to a salary dispute with CBS. Kim had been seeking pay equality with fellow cast members Alex O'Loughlin and Scott Caan, but CBS's final offer to Kim was 10–15% lower than what O'Loughlin and Caan made in salary.
Grace Park as Officer Kono Kalakaua, (seasons 1–7). A former surfer, she was personally recruited by Steve McGarrett while still in her final days at the HPD Academy. She is the cousin of Lieutenant Kelly, and later becomes the wife of Adam Noshimuri. In the conclusion of the season 7 finale, Kono is seen aboard a flight to Carson City, Nevada, where it is later revealed she has since joined a task force aimed at combating sex trafficking. This was written into the show following Park's departure from the series in late June 2017 prior to the start of production of the eighth season due to a salary dispute with CBS. Park had been seeking pay equality with stars Alex O'Loughlin and Scott Caan, but CBS's final offer to Park was 10–15% lower than what O'Loughlin and Caan made in salary.
Taryn Manning as Mary Ann McGarrett, (season 1; guest seasons 2–4, 6 & 9) Steve's younger sister who lives in Los Angeles and occasionally visits Hawaii. At the beginning of the series she and Steve are largely estranged from each other, but as time goes on gradually begin to make amends. Mary works various odd jobs including flight attendant and caregiver before adopting a baby girl whom she names Joan (later nicknamed 'Joanie') after their father.
Masi Oka as Dr. Max Bergman (seasons 2–7; recurring season 1; guest season 10), the eccentric and well-respected County of Honolulu medical examiner. He departs the series midway through season 7 upon joining Doctors without Borders in Africa.
Lauren German as Special Agent Lori Weston (season 2; guest season 2). A senior DHS agent assigned to Five-0 to provide oversight.
Michelle Borth as Lieutenant Catherine Rollins, USNR (seasons 3–4; recurring seasons 1 & 6; guest seasons 2, 5 & 7–10). A former Navy Intelligence officer and McGarrett's girlfriend.
Chi McBride as Captain Lou Grover, (seasons 4–10; guest season 4). A transfer from Chicago PD who has two children with his wife Renée.
Jorge Garcia as Special Consultant Jerry Ortega (seasons 5–10; recurring season 4), a conspiracy theorist who assisted Five-0 during several investigations and was eventually hired as a "consultant".
Meaghan Rath as Officer Tani Rey (seasons 8–10), whom McGarrett recruits from her job as a hotel pool lifeguard after being kicked out of the police academy, despite being a first-rate candidate. She initially declines to join but later becomes a team member.
Taylor Wily as Kamekona Tupuola (seasons 8–10; recurring seasons 1–7), a rehabilitated ex-convict, turned entrepreneur and owner of the Waiola Shave Ice, Kamekona's Shrimp Truck, and Kamekona's Helicopter Tours. He is a CI for the Five-0 Task Force and their friend.
Dennis Chun as Sergeant Duke Lukela (seasons 8–10; recurring seasons 1–7), HPD officer who often acts as a liaison to Five-0. He was one of the few HPD cops who was not antagonistic towards Danny or the other Five-0 members from the beginning, as he was colleagues with Steve's father and also personally knew Chin and Kono's family. In "Hookman", he was shot by Curt Stoner (Peter Weller), but survived and recovered. Dennis Chun is the son of Kam Fong Chun, who played Chin Ho Kelly in the original series.
Kimee Balmilero as Dr. Noelani Cunha (seasons 8–10; recurring season 7), a medical examiner who took over to assist the team after Max's departure. She is often seen joining in with the team during holidays and celebrations.
Beulah Koale as Officer Junior Reigns (seasons 8–10), a former Navy SEAL ranked Special Warfare Operator Second Class who asks McGarrett, a fellow SEAL, for a job. Initially turned down he returns to McGarrett a second time. McGarrett later introduces him to Duke Lukela and informs him that before becoming a member of Five-0 he will need to join and finish the police academy.
Ian Anthony Dale as Adam Noshimuri (seasons 8–10; recurring seasons 2–7), a member of the Five-0 Task Force; formerly the Head of Five-0 Task Force Special Division of Organized Crime; Kono's ex-husband, and a confidential informant to Five-0.
Katrina Law as Sergeant Quinn Liu (season 10), a former staff sergeant with Army CID demoted for insubordination.
