Final answer:
The first author to excel at both writing and illustrating picture books is not clearly defined, but John Audubon's 'The Birds of America' demonstrates early excellence in illustration combined with text.
Step-by-step explanation:
Early Excellence in Writing and Illustrating Picture Books
Identifying the first author to excel at both writing and illustrating picture books is challenging, as the development of children's literature involves various contributions over the centuries. However, an early and notable figure in the field of naturalist illustration is John Audubon, who was renowned for his influential work 'The Birds of America,' first published in 1827. Although Audubon's illustrations primarily focused on birds and not the standard picture book narrative, his combined talents in illustrating and writing set a precedent for future authors and illustrators in the genre. In the domain of children's fiction, where both text and images are essential, there are many significant contributions from different authors and illustrators that shaped the genre, like the Brothers Grimm with their collections of folktales.
However, it is the mid to late 19th and early 20th century which saw the rise of the picture book as we know it today. It is significant to mention that children's literature became a genuine literary genre during the first half of the 20th century, with celebrated authors like J.R.R. Tolkien and C.S. Lewis. While there is no definitive answer to who was the first to excel at both writing and illustrating, these examples show the progressive development of authors mastering both arts in children's literature.