Long Tailed Macaques (Macaca fascicularis) 

Long Tailed Macaques (Macaca fascicularis)
are found in Peninsular Malaysia and much of Southeast Asia.
While incredibly intelligent, being known to employ tools among other things, they are sometimes notorious for aggressively stealing items in return for food. Long Tailed Macaques are best observed from a distance and as much as possible direct eye contact is avoided.
Unfortunately due to habitat loss and troublesome interactions with humans, populations of Long Tailed Macaques are declining and they are currently assessed as Endangered by the IUCN Conservation Status.