The Clangers originated in a series of children's books which originated from another Smallfilms production, Noggin the Nog. Publishers Kay and Ward created a series of books from each of the Noggin the Nog episodes, which were then extended into the series called Noggin First Reader, a series aimed at aiding initial reading skills.
In the 1967 published story Noggin and the Moonmouse, a new horse-trough was put up in the middle of the town in the North-Lands. A spacecraft hurtled down and splashed into it. The top unscrewed, and out came a largish, mouse-like character in a duffel coat, who wanted fuel for his spacecraft. He showed Nooka and the children that what he needed was vinegar and soap-flakes. So, they filled up the various tanks in this little spherical ship, which then "took off in a dreadful cloud smelling of vinegar and soap-flakes, covering the town with bubbles".
In 1969, the BBC asked Smallfilms to produce a new series for colour television, but did not specify any particular storyline. Postgate concluded that because space exploration was particularly topical, the new series should be set in space. He adapted the Moonmouse from the earlier story, removing its tail "because it kept getting into the soup". The Clangers looked similar to mice, anteaters and, from their pink colour, pigs. They wore clothes reminiscent of Roman armour, "against the space debris that kept falling onto the planet[,] lost from other places, like television sets and bits of an Iron Chicken", and they spoke in whistles.