In Germany there’s a bunch of extremely popular and famous audio book series.
It probably peaked about 30-20 years ago when every kids room got a tape recorder and a bunch of cassettes. Today many adults still listen to the stories from their youth and today’s generation got players such as a toniebox that replaced cassettes and cds. Stories are usually between 30-60min in length and about the main character and their friends making the world a better place.
To name a few series:
Benjamin Blümchen
Bibi Blocksberg
Die drei ???
TKKG
Is there a comparable phenomenon in other countries? What are popular series, which group do they target and what are typical genres?