When Trevor arrived at the RSPCA in April he was severely emaciated, mostly deaf and with little hope left.
Today he stands proud, a hero in the eyes of his new owners after he chased away a burglar from their Thornlie home on Saturday.
Li Ye and Zhuofang Zhuo are proud of their two-year-old Staffordshire bull terrier which, despite his hearing loss, sensed a stranger in their home about 2.30am.
Trevor, who is normally placid, startled the burglar and woke his owners.
"Trevor felt threatened and the noise he made was like he was going to attack something or like he was trying to warn us," Mr Ye said.
Trevor knocked on Ms Zhuo's door, but she ignored him, so he went into action.
He terrified the would-be thief enough that he locked himself in the bathroom before fleeing out a window.
"He is normally friendly to strangers," Mr Ye said.
When the friends checked their home, they found a few things disturbed but nothing was stolen.
Trevor was well underweight at just 14kg when rescued by the RSPCA but he is on the mend and has gained at least 6kg since settling into his new home.
RSPCA spokesman Tim Mayne said Trevor's story highlighted the remarkable things animals surprised their owners with.
"They can be our constant companions and protectors," he said. "Trevor came from appalling conditions and his story demonstrates remarkable resilience.
"Animals can bounce back from neglect and become happy, healthy pets."