Which process in the body is primarily controlled by testosterone?

The hormone that stimulates the development of secondary sexual characteristics in males is called testosterone. Though this steroid hormone is mainly produced in the testes, it can also be produced in the ovaries and the adrenal cortex, but only in smaller amounts. 

Testosterone levels in males are responsible for their sex drives and play a vital role in sperm production. Aside from this, it can also affect bone and muscle mass, fat storage, red blood cell production and moods of males.