Killer was an 11-year-old Belgian malinois who worked alongside the Kruger National Park’s elite Special Operations Team. He spent eight years in South Africa tracking down poachers who often aimed their guns at him to avoid being caught.
In 2016 Prince Harry praised his work after he was awarded the animal equivalent of the George Cross by Ricky Gervais.
Harry met Killer in person the year before on a trip to Kruger National Park.
In that same year, the dog also made history when a South African judge said he would authorise his “testimony” as requested by handler Amos Mzimba.
The case resulted in two poachers being convicted thanks to Killer’s participation.
Mr Mzimba and Kruger’s K9 unit manager Johan de Beer stayed with Killer until his last moments.
Mr de Beer said: “Killer was one of the first anti-poaching dogs we had but his work out in the wilds had taken its toll on his back legs and he was in a lot of pain.
“There are a lot of people who will be sorry to hear of his passing, including Prince Harry, but it was time to let him go.
“His ashes will be taken to a special place out where he loved to be.”
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“He and Amos came under fire many times but he was clever and brave and always kept the scent and took down the poacher.
“They threw down chillies to put him off but it never worked and he kept going and going until he got his man. Rest in peace, Killer. You will be sorely missed, old friend.”
The outstanding dog was awarded the PDSA Gold Medal in 2016 for his work battling crime.
The award is the highest accolade a non-military animal can receive for its hard work.
PDSA Director General Jan McLoughlin said Killer was “a very worthy recipient” of the medal.
“His contribution to saving the rhino population has been truly remarkable.”
In a 2016 Facebook tribute, comic Ricky Gervais said: “K9 Killer is a scary name but this lovely boy does fantastic work in the Kruger National Park.
“His job is to help rangers track down poachers who kill native rhinos for their valuable horns.
“Thanks to his amazing courage and dedication, Killer has helped catch dozens of poachers and is making a huge contribution to rhino protection.”
Killer spent his first year in a special training programme, followed by 16 months in the Kruger National Park practicing to track human scent only.