At the beginning of The Boy in the Striped Pajamas, when Bruno and his family are living in Berlin, he has three close friends: Karl, Daniel, and Martin.
Karl’s father is a greengrocer, and he runs a shop “in the center of town,” which Bruno has presumably visited many times. Daniel’s father is a teacher who taught boys older than Bruno. This is easy for Bruno to remember, because he knows to “steer clear” of the boys taught by Daniel’s father. Martin’s father is a chef and would sometimes fetch his son from school wearing “a white smock and a tartan apron.” On these occasions, Bruno realizes that he has come straight from work to fetch his son. In contrast with his three friends, who understand precisely what their fathers do for a living, Bruno is unsure what his own father does for a living. The detailed explanations of the jobs that his friends’ fathers did provides a telling contrast with the unknown activities of Bruno’s father.
After Bruno’s family relocates so that his father can continue to do his mysterious job, Karl, Daniel, and Martin eventually become a distant memory for Bruno. His new friend, the titular “boy in the striped pajamas,” is Shmuel. Prior to his incarceration in the concentration camp, Shmuel’s father had been a maker and repairer of watches. He once gave his son a “beautiful watch” which, like so many other things, was stolen from Shmuel by the soldiers.