The protagonist of A Dog’s Purpose is a dog who has many names throughout the novel. The dog begins his first life in difficult circumstances (as a wild puppy taken to an illegal rescue) and quickly begins to search for purpose. The dog’s first life ends tragically early, and he never truly finds a purpose; however, he understands that humans are an important factor in the health and happiness of dogs, a lesson he will carry with him through his next lives.

It is in his second life, as Bailey, that the dog begins to learn most of the lessons that will inspire his later incarnations. Bailey’s life once again begins traumatically (being taken and left in a hot car) and almost ends in death, but he is saved by someone, a fact that underscores the lesson he learned in his first life—that humans are generally good. Bailey becomes the dog of an eight-year-old boy named Ethan and begins to learn the lessons of a domesticated animal, such as how to behave and when. In this life, Bailey must also learn to coexist with a cat, a lesson that will also play a role in a later incarnation.