Based on what the book describes Junior as a scrawny kid with "too much spinal fluid" in his brain. Also, the author gives us a drawn cartoon of Junior which looks to be a fragile person with a big head.
Based on the book, we learn that Junior likes to draw different types of cartoons about his life (like himself, his family, his friends, people that he meets, etc.)
Based on the book, Junior's personality is wit and humor. The book shows that Junior takes on his life with humor even if some things are keeping him down like during the basketball game against Wellpinit, Junior started laughing about an ironic thing that happened where all the indians turned his back on him, all the same time.
Based on the book, Junior dreams to make it somewhere in life, to break that cycle of staying in the reservation and poverty. Junior wants to change that. hence him going to Reardan, believing that is the first step to breaking the cycle.