The first Dell issue of "Lassie" brought the Rocky and Gerry stories of the Dell "M-G-M's Lassie" series to an end. Timmy was introduced in the third issue in a story based on his September 1957 television debut. Other "Lassie" comic book stories were sometimes based on episodes of the television series.
Many of the regular cast members of the television series migrated to the comic book series, including farmboy Jeff Miller, his mother Ellen and his paternal grandfather "Gramps" Miller, his chubby friend Porky Brockway and Porky's basset hound Pokey, Calverton veterinarian Doc Weaver, Timmy Martin and his adoptive parents Ruth and Paul Martin, and Paul's uncle Petrie Martin.
All front covers in the Dell series are color photographs depicting either Lassie alone or Lassie and Timmy (CBS child star Jon Provost). Secondary features include one-page text stories with canine themes and four-page comics stories about Blaze, a yearling colt being trained as a polo pony. When the Dell series expired, Western picked up the Timmy and Lassie stories for five issues with Lassie and the Martin family living in Africa.