Perth Zoo is in mourning following the tragic death of Hsing Hsing, their oldest male Sumatran orangutan.
A crowd favourite known for his dreadlocks and booming voice, Hsing Hsing succumbed to diabetic complications over the weekend.
The 42-year-old was diagnosed with diabetes at 21.
Keepers trained Hsing Hsing to present his arm daily for insulin injections and have his blood sugar levels tested regularly.
With his condition deteriorating over the weekend, the heartbreaking decision was made to give Hsing Hsing a "dignified end to life", according to Perth Zoo.
"Hsing Hsing was a very special member of the Perth Zoo family and will be greatly missed," a zoo spokesperson said.
"[His] formidable presence enforced his position as the dominant male in the 10-strong colony."
Hsing Hsing was born in 1975 at Singapore Zoo, the same year critically endangered Sumatran orangutans were afforded the highest degree of protection against international trade.
Numbers in the wild continue to decline however, with loss of habitat and the illegal wildlife trade threatening remaining orangutans.
Perth Zoo asked anyone wishing to mark Hsing Hsing's passing to make a donation to the zoo's Wildlife Conservation Action in lieu of flowers.
Proceeds will help Hsing Hsing's critically endangered wild cousins in Indonesia.
