Sumatra
Sumatra (Indonesian: Sumatera) is an island in western Indonesia and part of the Sunda Islands. It is the largest island that is entirely in Indonesia (two larger islands, Borneo and New Guinea, are shared between Indonesia and other countries) and the sixth largest island in the world at 480,847.74 km2
(including adjacent islands such as the Riau Islands and Bangga
Belitung Islands), with a current population of over 50 million (54
million administratively, as Riau Islands and Bangka–Belitung Islands are included). Its biggest city is Medan which has over 4,300,000 people in its metropolitan area.

Settler colonies began arriving in Sumatra around 500 BC, and several significant kingdoms flourished there. I Ching, a Chinese Buddhist monk, studied Sanskrit and spent four years of his life working in Palembang. The explorer Marco Polo visited Sumatra in 1292.
Eighty-seven percent of Sumatrans are thought to be Muslim. The island is home to 22% of Indonesia's population.
Sumatra has a huge range of plant and animal species but has lost
almost 50% of its tropical rainforest in the last 35 years, and many
species are critically endangered such as the Sumatran Ground-cuckoo, Sumatran tiger, Sumatran elephant, Sumatran rhinoceros, and Sumatran orangutan. Deforestation on the island has also resulted in serious haze over neighbouring countries, such as the 2013 Southeast Asian haze causing considerable tensions with affected countries such as Singapore and Malaysia.
source ; http://en.wikipedia.org/wiki/Sumatra