The young narrator of To Kill a Mockingbird by Harper Lee is Jean Louise ("Scout") Finch; her older brother is Jem Finch. They are the daughter and son of Atticus Finch, and they live in Maycomb, Georgia.
We meet Jem in the opening lines of the novel, where we learn his age at the time (thirteen) from Scout who is looking back at the events recorded in the book. During the year Jem was thirteen, his arm got broken at the elbow and, like many teenage boys would have been, he was worried that he would never be able to play football again; however, he soon recovered.
His left arm was somewhat shorter than his right; when he stood or walked, the back of his hand was at right angles to his body, his thumb parallel to his thigh. He couldn’t have cared less, so long as he could pass and punt.
Throughout the novel, Jem is Scout's partner in crime, her bossy big brother, and her companion.