Their long arms which make them well suited to their treetop lifestyle.
They measure between 115-137cm tall and weigh between 40-90kg.
Fruit and leaves make up around 60% of their diet. They eat a lot of food and sometimes spend whole days gorging on fruit.
They spend most of their time living in the trees in the lowlands of Borneo.
There are approximately 55,000 Bornean orang-utans in the wild.
Habitat loss, drought and fire.
Like us, orang-utans will often use tools to help them and have been spotted using leafy tree branches to shelter them from the rain like an umbrella.
Listen to a Bornean orang-utan.
Watch an orang-utan in a video from our friends at ARKive