Alex O'Loughlin as Lieutenant Commander Steven "Steve" McGarrett, USNR, a former Navy SEAL with time spent in Office of Naval Intelligence. He is named after his grandfather, a USS Arizona casualty. McGarrett's father John is murdered in the pilot episode, and this forms the basis for the series' first story arc. (In the Season 2 episode 14, "Pu'olo", it was revealed that John McGarret was born on March 15, 1942, and died September 20, 2010.) Steve McGarrett is both physically and intellectually capable, being able to speak Hawaiian and Chinese fluently while also being able to engage a person in hand to hand combat as well as utilizing fieldcraft when needed. McGarrett utilizes close quarters combat as his primary means of taking down suspects, something he was taught during SEAL training. He is an experienced Navy SEAL, as the governor once outlined his resume "Annapolis, five years Naval Intelligence, six years with the SEALs. Your superiors say that you are the best they have ever seen."

Scott Caan as Detective Sergeant Daniel "Danny" (or "Danno") Williams, a Honolulu Police Department (HPD) detective, who transferred from the Newark Police Department when his ex-wife, Rachel, moved to Hawaii with their daughter Grace. Williams' "by-the-book" style contrasts with McGarrett's more impulsive "the ends justify the means" approach, and is a source of friction (and banter) between the two. Regarded as a haole for wearing a tie on the island during the first season, Williams is a loyal cop who is married to his job first and life second. As a consequence, he is often at odds with his ex-wife Rachel for sometimes not being on time. He is a loyal cop and friend, once refusing to believe that his former police partner was corrupt even when pitted against overwhelming evidence after the partner was found dead.Daniel Dae Kim as Detective Lieutenant Chin Ho Kelly, a former ex-member of the HPD (reinstated in finale of season 1) and protégé of McGarrett's father, who left the force after being falsely accused of corruption. It is later revealed that his uncle, a retired cop, took the money to pay for medical bills for his aunt. Despite insistence that he come clean, Kelly is willing to take the blame to prevent his uncle from going to jail. He is eventually cleared of the corruption charges and is reinstated to the HPD as a Lieutenant, but returns to the task force.

Daniel Dae Kim as Detective Lieutenant Chin Ho Kelly, a former ex-member of the HPD (reinstated in finale of season 1) and protégé of McGarrett's father, who left the force after being falsely accused of corruption. It is later revealed that his uncle, a retired cop, took the money to pay for medical bills for his aunt. Despite insistence that he come clean, Kelly is willing to take the blame to prevent his uncle from going to jail. He is eventually cleared of the corruption charges and is reinstated to the HPD as a Lieutenant, but returns to the task force.

| 1x08 “Mana'o (Belief)”