Utan
... became an orphan at the age of 4 years and was adopted by a female of the group Duna. He was always lagging behind in his physical development and although he is now 17 years old, he never reached the size of a full grown adult male.
Read more about Utan and how he nearly lost his group here [pdf]
Click here to watch: "Utan eats driver ants"
(Video is taken by Tobias Deschner from the Taï Chimpanzee Project)