When biography first gained recognition as a genre for adults, it was not considered an appropriate form of literature for children. As it began to gain a place in children's literature, as was true of most books written for children at the time, biography was used as a tool for teaching children to emulate the hero.
Bowen, Dorothy N., "Using Biography in the Elementary Classroom" (2002). Curriculum and Instruction Faculty and Staff Scholarship. Paper 23.