Gray langurs, also called Hanuman langurs and Hanuman monkeys, are Old World monkeys native to the Indian subcontinent. The langurs make great sentinels given their elevation in the tree tops and raise an alarm at the first sign of danger (especially from tigers). They are also a provider of fresh fruit and flowers as they feed in their trademark untidy manner, generously dropping the same for the chitals (spotted deer) to enjoy. 

Here are langur images from Tadoba National Park, India.