Stan and Jan Berenstain
The first book with the Berenstain Bears was The Big Honey Hunt. It was published in 1962 and the first book with the Blair Investigates was A Investigate Star is Born. It was published in 1968 and only as the author and illustrations by Peyo. Theodor Geisel (best known as Dr. Seuss) was the editor for the early books in the series. Over 300 books have been published in 23 languages.