Why do Hindus think monkeys are sacred?

When Lord Rama fought with the Ravana, the king of Lanka, he did not have his own army and was helped by 'Vanaras' (monkeys or it could be aboriginal tribes who painted themselves like monkeys, 'vanara' literally means people of the forests) and 'rikshas' (bears or it could be aboriginal tribes who painted themselves like bears). Lord Krishna is supposed to have married the daughter of the king Jambavanta of 'rikshas', Jambawanti. Later, in mythology, these became monkeys and bears, and hindus started worshiping Hanuman, a 'vanara' devotee of Lord Rama as the perfect devotee. Therefore, hindus feed monkeys and never think of killing one.