Tareq Kamleh, an Australian doctor, appeared in ISIS propaganda videos encouraging others to join

His diary was discovered in a house that had been set up for him in Raqqa, revealing his "despair" about ISIS

Kamleh complained about ISIS militants being cruel to animals, albeit condoning the fact they murder people

Whether Kamleh is dead or alive or where he might be hiding was not clear

Tareq Kamleh was the poster boy for ISIS - an Australian doctor happily serving in Syria and encouraging others to join him. But behind the slick propaganda videos, the former Perth pediatrician was increasingly in "despair" about the caliphate's direction.

His unhappiness was revealed in a diary that was discovered in a house set up for him in Raqqa.

Macer Gifford, a former British currency trader fighting with a Kurdish militia who found the diary, said he frequently complained about the terrorist group.

"I don't think he was a particularly happy character... He didn't seem to be getting on with people there very much," he told Fairfax.

Gifford, who goes by a pseudonym, said his exact words at one point were: "I despair for the future of the caliphate".

Central to Kamleh's disillusionment was his fellow jihadist's refusal to donate to an orphanage he became involved with, and the lack of support from commanders.

He also complained about ISIS fighters being cruel to animals, such as beating dogs, which upset him despite the murder and destruction he otherwise condoned.

"Of all the things that ISIS has done, brutally murdered people and blown up homes, here was a guy who, it seemed, had had half his brain removed. Half of it was dedicated... but his sense of empathy, right and wrong, was way off," Gifford said.

"He was almost completely directionless as a person, wanting to cling to [ISIS] yet writing very openly and clearly how much he despaired at it."

Gifford handed over the notebook diary to Kurdish military collecting intelligence for U.S. forces, but said other documents showed the house was Kamleh's.

They included measurements for a uniform, a note transferring its ownership to him, and a stamped document with a letterhead instructing an armory to give him and another fighter gun holsters.

Gifford likened Kamleh to American Psycho character Patrick Bateman - a charismatic obsessed with his appearance and health but psychotic.

He made notes about how many pushups he planned to do, and wrote about his military training in meticulous detail - even doodling AK47 rifles.

"Just a neat, intelligent but slightly psychopathic character is what came across in his possessions," Gifford said.

This squared with statements from former colleagues in Australia who said he was charming but manipulative and sexually predatory.

Whether Kamleh is dead or alive or where he might be hiding was not clear but most foreign fighters were believed to have fled Raqqa before it fell.

With ISIS effectively defeated after its last stronghold fell earlier this month, he may have been killed elsewhere or still be on the run.

This article has been adapted from its original source.