Which hormone is primarily responsible for the development of male secondary sexual characteristics?

Testosterone is the hormone predominantly responsible for the development of male secondary sexual characteristics. These characteristics include the development of facial and body hair, increased muscle mass, deepening of the voice, and the growth of the Adam's apple. Testosterone plays a crucial role during puberty by promoting these changes which define male physical characteristics and contribute to sexual maturity.

This hormone is primarily produced in the testes and is essential for not only the development of secondary sexual traits but also for maintaining muscle and bone health throughout life. Its effects are mediated through androgen receptors in target tissues, which lead to the various physiological changes associated with male maturation and health.