Walt Lloyd (Malcolm David Kelley) is a boy stranded on a mysterious island, after the crash of an Oceanic airliner. He is traveling from Australia to Los Angeles with his biological father, Michael (Harold Perrineau), a man he barely knows. Michael takes custody of Walt after the death of Walt's mother, who left Michael when Walt was just a baby.
Walt copes well with being on the island, and has his dog, Vincent, for company. He struggles with taking orders from his father, who is trying to forge a relationship with him. Walt becomes friends with John Locke (Terry O'Quinn), and starts to spend a lot of time with him. Michael is jealous of this relationship and warns Walt to stay away from Locke. Locke recognizes something special in Walt, and tries to give Michael advice on how to relate to his son, however, Michael does not listen, and his relationship with Walt remains rather distant and awkward.
A pivotal moment occurs when Walt secretly burns the raft his father is building to get the passengers off the island. Walt does not want to leave the island, because he is afraid of what a new life with his father might bring. Walt admits his wrong doing, and the raft is rebuilt. Walt sets off with Michael and a few other passengers on the raft, in hopes of finding rescue. Suddenly, the raft is overtaken by a boat, and Walt is kidnapped by the mysterious "Others", who also inhabit the island.
After Michael strikes a tragic deal with the leader of the Others, he and Walt get off the island and head to the United States. The events he experienced on the island continue to follow Walt, and he eventually goes to live with his grandmother after he and Michael become estranged.
Walt is a key figure in "Lost" because he appears to Locke later on the island as a vision, and appears years later, after he has grown considerably, in the alternate world scenarios.
"Don't open it."
"Get up, John. You've got work to do."