After playing the original Lassie in 'Lassie Come Home' (1943), Pal was cast in the follow-up, 'Son of Lassie' (1945). He was cast as the title character, however, and another dog played Lassie!
Almost all dogs in the subsequent 'Lassie' films, and television series, have been descendants of Pal. The dog who played Lassie for the first half of season 2 of the 1997 Lassie series and the dog who played Lassie in the 2005 Lassie movie were not descendants of Pal.
The first dog to play the heroine 'Lassie' - although he was actually a male dog, not a bitch.