Lassie is a fictional female Rough Collie dog and is featured in a 1938 short story by Eric Knight that was later expanded to a 1940 full-length novel, Lassie Come-Home. Knight's portrayal of Lassie bears some features in common with another fictional female collie of the same name, featured in the British writer Elizabeth Gaskell's 1859 short story "The Half Brothers". In "The Half Brothers", Lassie is loved only by her young master and guides the adults back to where two boys are lost in a snowstorm.

The Rough Collie is a long-coated dog breed of medium to large size that, in its original form, was a type of collie used and bred for herding sheep in Scotland. More recent breeding has focused on the Collie as a show dog, and also companion. The breed specifications call for a distinctive long narrow tapered snout and tipped (semiprick) ears, so some dogs have their ears taped when young. Rough Collies generally come in shades of sable and white, blue merle, tri-coloured, and colour-headed white.