Here is a fun link with a video:

Dogs really are man’s best friends. But maybe they’re just best friends in general. It’s hard to think of more unlikely buddies than these? Roscoe is playful old hound dog. Suryia is an equally playful orangutan.

Suryia lives in an endangered species habitat in South Carolina. Roscoe was a stray. They met while Suryia taking a walk with his handlers. They saw each other. They approached each other. And they played. Their friendship was instantaneous. When it was time to go home, Roscoe followed.

http://videos.komando.com/2009/09/29/the-orangutan-the-hound-dog/