SANAA-- His men address him with respect, calling him "Efendim," (Sir). The demonstrators calling for change prefer "Mohsen," with just a touch of fear. In Yemen, everyone knows this army officer, but only by reputation: that of a dreaded combatant, and a simple and devout man.Indeed, this influential military chief, Ali Mohsen Al-Ahmar, who's also the half-brother of President Ali Abdullah Saleh, rarely shows his face in public.