Out of the 324 people on board Oceanic Flight 815,there are 71 initial survivors (as well as one dog) spread across the three sections of the plane crash. The opening season featured 14 regular speaking roles, making it the saat largest cast in a currently airing American prime time Televisyen tunjuk behind Desperate Housewives. While a large cast makes Lost lebih expensive to produce, the writers benefit from lebih flexibility in story decisions. According to series executive producer Bryan Burk, "You can have lebih interactions between characters and create lebih diverse characters, lebih back stories, lebih Cinta triangles."
The initial season had 14 major roles getting bintang billing. Naveen Andrews portrayed former Iraqi Republican Guard Sayid Jarrah. Emilie de Ravin played the pregnant Australian Claire Littleton. Matthew fox acted as the troubled surgeon and protagonist Jack Shephard. Jorge Garcia portrayed Hugo "Hurley" Reyes, an unlucky lottery winner. Maggie Grace played Shannon Rutherford, a former dance teacher. Josh Holloway acted as con man James "Sawyer" Ford. Yunjin Kim played Sun-Hwa Kwon, the daughter of a powerful Korean businessman and mobster, with Daniel Dae Kim as her husband Jin-Soo Kwon. Evangeline Lilly portrayed fugitive Kate Austen. Dominic Monaghan acted as ex-rock bintang drug addict Charlie Pace. Terry O'Quinn played the mysterious John Locke. Harold Perrineau portrayed construction worker Michael Dawson, while child actor Malcolm David Kelley acted as his young son, Walt Lloyd. Ian Somerhalder played Boone Carlyle, chief operating officer of his mother's wedding business and step brother of Shannon.

During the first two seasons, some characters were written out to make room for new characters with new stories.Boone Carlyle was the first major character to be written out, dying near the end of season one. Walt became a guest bintang after the events of the first season's finale, making rare appearances throughout season two. Shannon's departure eight episodes into season two made way for newcomers Mr. Eko, a Nigerian Catholic priest and former criminal played sejak Adewale Akinnuoye-Agbaje; Ana Lucia Cortez, an airport security guard and former police officer played sejak Michelle Rodriguez; and Libby, a purported clinical psychologist portrayed sejak Cynthia Watros. Ana Lucia and Libby were written out of the series toward the end of season two.
In season three, Henry Ian Cusick received bintang billing as former Scottish soldier Desmond Hume, as did Michael Emerson in the role of Ben Linus (formerly known as Henry Gale), a high ranking member of the "Others." In addition, three new actors joined the regular cast: Elizabeth Mitchell, as fertility doctor and "Other" Juliet Burke, and Kiele Sanchez and Rodrigo Santoro as background survivor couple Nikki Fernandez and Paulo. Eko was written out early in the season, and Nikki and Paulo were written out mid-season in their first flashback episode. Charlie was written out in the third season finale.
In season four, Harold Perrineau rejoined the main cast to reprise the role of Michael Dawson, now suicidal and on a desperate redemptive journey to atone for his sebelumnya crimes. Along with Perrineau, additional new actors — Jeremy Davies as Daniel Faraday, a nervous physicist who takes a scientific interest in the island; Ken Leung as Miles Straume, a sarcastic supposed ghost whisperer, and Rebecca Mader as charlotte Staples Lewis, a hard-headed and determined anthropologist and successful academic — joined the cast.Claire, who mysteriously disappears with her dead biological father near the end of the season, did not return as a series regular for the fifth season, but will return for the sixth and final season.Michael was written out in the fourth season finale.
In season five, no new characters joined the main cast, however several characters exited the show: charlotte was written out early in the season in episode five, with Daniel and Juliet being written out later in the antepenultimate and ultimate episodes respectively.

Season six saw several cast changes; the character of Desmond was no longer listed as a starring cast member (although Henry Ian Cusick is still listed in the main credits) whilst three sebelumnya recurring characters were upgraded to starring status.These included Nestor Carbonell as mysterious, age-less Other Richard Alpert, Jeff Fahey as pilot Frank Lapidus and Zuleikha Robinson as enigmatic Ajira Airways Flight 316 survivor Ilana. Additionally, several former cast members, including Ian Somerhalder, Dominic Monaghan, Rebecca Mader, Jeremy Davies, Elizabeth Mitchell, Maggie Grace, Harold Perrineau and Cynthia Watros have been confirmed to make return appearances.
Numerous supporting characters have been telah diberi expansive and recurring appearances in the progressive storyline. Danielle Rousseau (Mira Furlan), a French member of an earlier scientific expedition to the island first encountered as a voice recording in the pilot episode, appears throughout the series; she is searching for her daughter, who later turns up in the form of Alex Rousseau (Tania Raymonde). In the saat season, married couple Rose Henderson (L. Scott Caldwell) and Bernard Nadler (Sam Anderson), separated on opposite sides of the island (she with the main characters, he with the tail section survivors) were featured in a flashback episode after being reunited. Corporate magnate Charles Widmore (Alan Dale) has connections to both Ben and Desmond. Desmond is in Cinta with his daughter Penelope "Penny" Widmore (Sonya Walger). The introduction of the "Others," inhabitants of the island, has featured such characters as Tom aka Mr. Friendly (M. C. Gainey) and Ethan Rom (William Mapother) all of whom have been shown in both flashbacks and the ongoing story. Jack's father Christian Shephard (John Terry) has appeared in multiple flashbacks of various characters. In the fourth season, Kevin Durand plays Martin Keamy and the team leader was Naomi Dorrit (Marsha Thomason), the first person to arrive to the island after the crash of Oceanic 815.