The series tells the adventures of the bearcub Rasmus Klump and his friends: Pingo (a penguin), Pelle (a pelican), Pildskadden (a turtle), Skæg (a seal) and others.

Always dressed in red dungarees with white polka dots, Rasmus Klump travels the world on board his boat Mary, which he builds with his friends in the first episode.

The comic strips do not make use of speech balloons but rather captions, whose humour, as well as the affectionately drawn pictures, contributed greatly to the popularity of the series.

Rasmus Klump began as a newspaper strip in Berlingske Aftenavis (now Weekendavisen) on 17 November 1951 and was successfully published in translation worldwide, with total sales running over 30 million.

In 1984, a new series of 13 episodes was produced, as a deal between PIB Copenhagen and Casterman in Belgium, and was animated by an American living in Japan.