Lennox, an illegal pit-bull terrier type dog, has been put down, Belfast City Council has confirmed.
The dog, which was put down on Wednesday after the expiry of a midnight deadline for legal appeals, attracted a global campaign of support.
Campaigners claimed to have 200,000 signatures supporting a reprieve and emotions were running high.
Staff at Belfast City Council were targeted for intimidation by some supporters.
One Belfast councillor has received a death threat over Lennox's proposed destruction and workers in Belfast City Council have become the target of a fresh series of intimidating and threatening messages.
Some Northern Ireland vets said they had been inundated with emails from campaigners.
One leading Northern Ireland veterinary surgeon said the emails being sent to individual vets and practices were causing problems.
"No doubt those campaigners feel this is justified as a means of advancing their aims," the vet said.
"However, I have now heard of two practices where test results for critically-ill animals failed to reach the vet as their mailbox was full of Lennox letters.
"I am sure that disrupting the treatment of other animals was not the intention of the campaigners, but I am afraid that is what is happening."
Lennox was impounded by Belfast City Council's dog wardens in 2010.
In June, Northern Ireland's most senior judges rejected Caroline Barnes' legal bid to overturn an order for the destruction of her pet.
Ms Barnes, who is disabled, and her family, insisted that Lennox was not dangerous. While it was not clear exactly what breed he was, pit bulls and dogs like them are illegal in Northern Ireland and in the rest of the UK.
'Danger to public'
Two lower courts had already ruled that the dog should be put down.
The dog was seized by Belfast City Council dog wardens in May 2010. He was assessed to be a danger to the public and subsequently ordered to be put down.
A former Metropolitan Police dog handler claimed the dog represented a danger due to his unpredictability.
Ms Barnes, 35, had accepted her pet was a pit-bull type, but claimed there had been a failure to properly consider a possible exemption scheme.
Her battle for Lennox became an international campaign to save his life. It went "viral" on social media websites and attracted tens of thousands of well-wishers.
Well-known people including boxer Lennox Lewis and Northern Ireland First Minister Peter Robinson were among those who used Twitter to call for the dog to be spared.
Some of the dog's followers took the campaign to extremes and Belfast council workers became the focus of intimidation and abuse.
Last year, threatening letters, one drenched in petrol, were put through the letter-boxes of two female dog wardens. Another staff member had her car tyres slashed outside her home.
In a statement on Wednesday, the council said: "Whilst there is an exemption scheme to which dogs of this type (pit-bull terrier type) may be admitted as an alternative to destruction, there were no such measures that could be applied in this case that would address the concerns relating to public safety.
"The council's expert described the dog as one of the most unpredictable and dangerous dogs he had come across."
Belfast City Councillor Pat McCarthy said several council staff had been intimidated.
"We've had dog wardens who had to leave their homes. We've had petrol poured through letter boxes, we've had people named on the web," he said.
"There have been attempts to demonize our staff for doing their job. The dog has now been put to sleep. It was deemed a dangerous dog.
"There was a court order for the dog's destruction and we had to carry it out.
"The people looking after Lennox for the past two years said that one minute the dog was placid and friendly and the next he would try to get through the fence to get at you.
"Now do we release that dog into society? We have a duty of care to people."
Television dog training expert Victoria Stillwell had offered to have Lennox re-homed in America where he would not be in contact with the public.
She said she was "absolutely devastated" that Lennox had been put down.
"I hoped Belfast City Council would realise that there were alternatives that provided a sanctuary for Lennox in the USA where he would be safe but they did not listen," she said.
"We asked the council that the family be allowed to see the dog before it was put down - they ignored that. They won't even allow the family to see the dog's body."
The two largest Northern Ireland veterinary associations said they believed the current legislation should change.
"We feel that dogs should be assessed on their deeds rather than their breed and this is the root of the problem.
"Our associations have continually made our views known to government on the Dangerous Dogs Legislation, however, it is also important that the public is adequately protected from genuinely dangerous dogs."