No, the author and illustrator are different people.
Illustrators help to make the illustrations that are used in books. They also help to create the designs for the covers and interior pages of a book.
Publishers generally do not provide illustrators, but they can often find artists who are willing to work on covers and interior designs.
An illustrator is someone who creates illustrations, typically for magazines and books.
Illustrators create illustrations while artists create art. Illustrators are often used in advertising, design, and illustration while artists are more commonly used in painting, sculpture, and architecture.