For months, Bon Bon the orangutan would lash out at any male who approached, after a Russian man drugged the animal, put him in a suitcase, and tried to smuggle him onto a flight from Bali.

Key points: Bon Bon's keeper Ketut Diandika was the only man to gain the animal's trust

Bon Bon's keeper Ketut Diandika was the only man to gain the animal's trust A Russian man is now in a Bali jail for trying to smuggle the orangutan to Vladivostok

A Russian man is now in a Bali jail for trying to smuggle the orangutan to Vladivostok Only around 13,400 Sumatran orangutans remain in the wild

The three-year-old Sumatran orangutan was so traumatised by the ordeal last March that keepers at Bali Safari Park gave him an orangutan "doll" as a substitute for his mother.

Bon Bon spent nine months rehabilitating at the park.

With patience, care and the help of two other orangutans, Bon Bon's keeper, Ketut Diandika, finally gained the animal's trust.

It was Mr Diandika who this week personally carried Bon Bon into a specially designed cage to relocate the primate to northern Sumatra, where it is hoped he can soon be returned to his natural habitat.

Mr Diandika will stay with Bon Bon for several days at the Sumatran Orangutan Conservation Program, to help the animal adapt to other orangutans — and a new carer — before he is released to the wild.

"We will ensure … he won't have the same experience as when he was separated from his mother, when he separates from his mate and keeper here at Bali Safari Park," said a senior vet at Bali Safari Park, Yohan Kusumaningtyas.

During the transitional period, conservation authorities in Sumatra will re-introduce Bon Bon to his natural food and environment.

All contact with humans — and the orangutan doll — will slowly disappear until Bon Bon again returns to his wild state.

Authorities can't predict how long the rehabilitation process will take, but say an orangutan's ability to build a nest in a tree is one sign of readiness.

Bon Bon after being confiscated in Bali, Indonesia last year. ( Antara Foto: Nyoman Hendra Wibowo via Reuters )

Bon Bon's journey from Bali Safari Park to Sumatra took nine hours, including road transport to Bali's Ngurah Rai airport, a flight to Jakarta and time in transit, then a second flight to Medan and another road trip to the Sumatran Orangutan Conservation Program at Batu Mbelin near Medan.

Before the trip Bon Bon was fed fruit, including bananas and rambutans. Vets travelling with the relocation team carried out health checks before the orangutan was placed inside the metal and wood box with the doll.

Mr Diandika continued to comfort Bon Bon until the cage was shut and the journey began. A sliding window in the box allowed Bon Bon to peep outside and take the odd piece of fruit.

The Sumatran orangutan (or Pongo abelii) is critically endangered from hunting, trafficking and habitat loss. It lives only in forest bordering Indonesia's northernmost province, Aceh, and North Sumatra.

Only about 13,400 Sumatran orangutans remain in the wild.

A 2018 comprehensive study of Borneo's orangutans estimated their numbers have plummeted by more than 100,000 since 1999, as the palm oil and paper industries shrink their habitat and fatal conflicts with people increase.

The orangutan was found sedated in a rattan basket. ( Supplied )

Andrei Zhestkov, a 27-year-old Russian national, has been jailed in Bali for trying to smuggle Bon Bon to his home in Vladivostok as a pet.

The orangutan was found sleeping in a rattan basket inside Zhestkov's suitcase. Airport authorities also discovered two geckos and four chameleon lizards.

Bali police said in March that Zhestkov confessed to them that he bought the orangutan for $US3,000 from a street market in Java.

Zhestkov had fed him allergy pills mixed with milk so he would lose consciousness for up to 10 hours on the flight home to Russia.

The Denpasar District Court sentenced Zhestkov in July to one year in prison and fined him 10 million rupiah.

Indonesian police said another three baby orangutans were recently taken from the wild and abandoned on a street in Sumatra's Riau province.