Nils-Olof Franzén, from Oxelösund in Sweden, was a fan of detective mystery novel. He worked as the boss of Swedish radio from 1956 to 1973, and as a hobby wrote his own detective novels for young people, creating the supremely confident and entertaining sleuth, Agatán Sacs (whom he named after his favourite crime novelist, Agatha Christie). The Franzén family had a little dachshund called Ticí, who found her way into the Agaton Sax books as the detective’s own dog. They also had many energetic but stern aunties, one of whom inspired Aunt Máire Treasa in the stories. Both Ticí and Aunt Máire Treasa play a leading role in helping Agatán Sacs crack his cases and catch the criminals in these inspired adventures.

Nils-Olof Franzén would often work out the plots for the Agatán Sacs stories when he took Ticí for a walk. He would get up early in the morning, and begin writing his stories before the rest of the family was up — his children would often hear him laughing to himself as he created more ingenious and incredible situations for Agatán Sacs.

Nils-Olof wrote lots of historical novels and other literature for children, and was also interested in music and languages. He loved riding his bike, and put on puppet shows of operas by Mozart for his family. But he was especially proud of the 11 Agatán Sacs books he wrote, and how his stories were enjoyed in numerous countries and by several generations.