Rick Marshall, his son Will and his young daughter Holly, were rafting on the Colorado River in the Grand Canyon when they were caught in "the greatest earthquake ever known." The river was diverted over a cliff, and as the Marshalls' raft plunged over the resulting waterfall they struck a time doorway partway down. Trapped in the Land of the Lost with only the minimal camping equipment they'd had on the raft, they make their camp in a natural cave partway up the face of a cliff they call the High Bluff.
The three of them are from California, though Rick grew up on Ford Street in Indianapolis and attended Fillmore High there. The Marshalls formerly lived in Harrisville, Indiana. Mrs. Marshall died of unspecified causes when Will and Holly were very young, and neither of them remembers her very clearly. Rick describes her as being headstrong and beautiful, just like Holly, and apparently loved her deeply. Will and Holly frequently suffer bouts of sibling rivalry, though they overcome such issues when the situation becomes difficult enough. Will is the most adventurous of the Marshalls, frequently taking "shortcuts" as an excuse to explore new territory and tampering with Pylons to determine their function. Holly suffers from a fear of heights.
At the beginning of the third season, Rick Marshall unexpectedly returns home via a time doorway in a newly discovered pylon; Will and Holly's uncle Jack Marshall, who had been searching for them for six months by following the same river route along which they'd originally disappeared, experiences another earthquake and falls through a doorway into the Land. At the same time, another earthquake occurs in the Land itself that buries High Bluff along with the Marshalls' equipment and provisions. Therefore, the Marshalls move into a temple near the Lost City instead (not the same as the Builder's Temple).
The series ends without showing the Marshalls' ultimate fate, though there are some ambiguous suggestions of it. In "Elsewhen," an adult version of Holly visits via a time doorway from the future, and in another episode a mysterious "repairman" confidently predicts that the Marshalls will someday escape the Land of the Lost.
An alternate universe version of the Marshalls (who wear clothing that "our" Marshalls lost upon entry into the Land of the Lost, and who did not suffer the loss of their mother) appear in "Split Personality." It is discovered in the last first-season episode[1] that the Marshalls were their own counterbalance; their death in the Land of the Lost in that episode is what causes the time doorway that drew them there in the first place to open. "Circle" was intended to serve as a "final episode" in the event that the show was not renewed, but since two more seasons were videotaped after this episode depicted their escape (including the seemingly incompatible substitution of Jack for Rick), much debate has ensued in the fan community over exactly what this paradox meant for the Marshalls.
In the 2009 movie, the three characters are substantially different. Although given names are retained, they are no longer related to each other, and dysfunctional personality traits are added for comic effect.