Wikia

Several characters have been played by different actors at different ages:

Character	Primary Portrayer	Second Portrayer	Third Portrayer	Fourth Portrayer	Notes
Kate Austen	Evangeline Lilly (ages 24-30)	Emily Rae Argenti (age 10)	Susan Goodwillie (voice in Lost: Via Domus)		Skye McCole Bartusiak provided the voice for 12-year-old Kate in the episode "Born to Run"
Tom Brennan	Mackenzie Astin (age 25)	Tanner Maguire (age 10)			Carter Jenkins provided the voice for 12-year-old Tom in the episode "Born to Run"
Juliet Burke	Elizabeth Mitchell (2001-2007)	Rylee Fansler (1970s/1980s)	Margaret Easley (voice in Lost: Via Domus)
Rachel Carlson	Robin Weigert (2001-2004)	Savannah Lathem (1970s/1980s)
Eko	Adewale Akinnuoye-Agbaje (ages 33-36)	Kolawolfe Obileye, Jr. (child)
Daniel Faraday	Jeremy Davies (ages 18-29)	Spencer Allyn (child)
James "Sawyer" Ford	Josh Holloway (ages 33-39)	Gordon Hardie (age 8)	Keegan Boos (age 8)		Sawyer was voiced by an unknown actor in Lost: Via Domus
Eloise Hawking	Fionnula Flanagan (ages 59-70)	Alice Evans (age 40)	Alexandra Krosney (age 17)
Charlie Hume	Marvin DeFreitas (age 2)	Unknown (newborn)
Jacob	Mark Pellegrino	Kenton Duty (age 13)	Unknown (newborn)
Omer Jarrah	Cas Anvar	Xavier Raabe-Manupule (child)
Sayid Jarrah	Naveen Andrews (ages ≤37-40)	Anthony Keyvan (age 8)			Sayid was voiced by an unknown actor in Lost: Via Domus
Steve Jenkins and Scott Jackson	Christian Bowman	Dustin Watchman
Ji Yeon Kwon	Jaymie Kim (child)	Unknown (newborn)
Sun-Hwa Kwon	Yunjin Kim (ages ≤24-27)	Sophie Kim (child)			Yunjin Kim also provided Sun's voice in Lost: Via Domus.
Charlotte Lewis	Rebecca Mader (age ≤33)	Maya Henssens (1977)	Unknown (1974)
Benjamin Linus	Michael Emerson (ages ≤39-40)	Sterling Beaumon (ages 9 & 11)	Amanda (newborn)		Michael Emerson also provided Ben's voice in Lost: Via Domus.
Aaron Littleton	William Blanchette (ages 0, 2-3)				Aaron was portrayed by 27 infants in the second season and 30 in the third, many hired as extras in case of emergency. Some of the 56 infants include Maddox Aherin, Sabrina Baker, Ella Renee de Coligny, Jade Heimowitz, Lily Loose, Julia Mueller, Emerson Reifsteck, Matthew David Viventi, and Josie Weinert. See Aaron Littleton#Casting for more information.
Walt Lloyd	Malcolm David Kelley (ages ≤10-13)	Unknown child actor (age 2)
Emily Locke	Swoosie Kurtz	Holland Roden (age 15)
John Locke	Terry O'Quinn (ages 39-48)	Charles Henry Wyson (age 5)	Caleb Steinmeyer (age 16)	Unknown (newborn)	Paul Eiding (voice in Lost: Via Domus)
Charlie Pace	Dominic Monaghan (ages ≤27-28)	Jeremy Shada (age 8)	Andrew Ableson (voice in Lost: Via Domus)
Liam Pace	Neil Hopkins	Zack Shada (child)
Hugo "Hurley" Reyes	Jorge Garcia (ages 20-25)	Caden Waidyatilleka (age 10)			Hurley was voiced by an unknown actor in Lost: Via Domus
Ethan Rom	William Mapother (age 27)	Devon Gearhart (teenager)	Unknown (infant)
Alex Rousseau	Tania Raymonde	Lehualani Silva (child)	Unknown (infant)
Danielle Rousseau	Mira Furlan (2004)	Melissa Farman (1988 - 1989)
Jack Shephard	Matthew Fox (<2001-2007)	John O'Hara (1970s)	Steve Blum (voice in Lost: Via Domus)
Marc Silverman	Zack Ward	Unknown (child)
Miles Straume	Ken Leung (ages ≤27-30)	Lance Ho (child)	Unknown (infant)
Tourniquet man	Dale Radomski	Kamakani De Dely
Vincent	Madison	Pono
Charles Widmore	Alan Dale	David S. Lee (age 40)	Tom Connolly (age 17)
Yemi	Adetokumboh McCormack	Olekan Obileye (child)